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A Whole Life Costing Approach for Rainwater Harvesting Systems Richard Roebuck PhD, Bradford University
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2.0 Rainwater Harvesting Literature Review
2.1 Introduction
Rainwater harvesting (RWH) primarily consists of the collection, storage and
subsequent use of captured rainwater as either the principal or as a
supplementary source of water. Both potable and non-potable applications are
possible (Fewkes, 2006). Examples exist of systems that provide water for
domestic, commercial, institutional and industrial purposes as well as
agriculture, livestock, groundwater recharge, flood control, process water and
as an emergency supply for fire fighting (Gould & Nissen-Peterson,1999; Konig,
2001; Datar, 2006). The concept of RWH is both simple and ancient and
systems can vary from small and basic, such as the attachment of a water butt
to a rainwater downspout, to large and complex, such as those that collect
water from many hectares and serve large numbers of people (Leggett et al,
2001a). Before the latter half of the twentieth century, RWH systems were used
predominantly in areas lacking alternative forms of water supply, such as coral
islands (Krishna, 1989) and remote, arid locations lacking suitable surface or
groundwater resources (Perrens, 1975). The fundamental processes involved in
rainwater harvesting are demonstrated in figure 2.1.
Figure 2.1 Flowchart demonstrating fundamental rainwater harvesting
processes
Production of runoff from catchment surface
Water storage in reservoir
Rainfall event(s)
Water use
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All rainwater harvesting systems share a number of common components
(Gould & Nissen-Peterson, 1999):
1. A catchment surface from which runoff is collected, e.g. a roof surface.
2. A system for transporting water from the catchment surface to a storage
reservoir.
3. A reservoir where water is stored until needed.
4. A device for extracting water from the reservoir.
Fewkes (2006) identifies the main uses for harvested rainwater as:
1. The main source of potable (drinking) water,
2. A supplementary source of potable water, or
3. A supplementary source of non-potable water, e.g. for WC flushing.
In developing countries the main use of harvested water is for potable supply
whilst in developed countries examples of all three uses exist, with potable
supplies being more common in rural locations and non-potable supplies in
urban areas.
2.2 A brief history of rainwater harvesting
Gould & Nissen-Peterson (1999) provide a detailed history of rainwater
harvesting systems. The authors state that, whilst the exact origin of RWH has
not been determined, the oldest known examples date back several thousand
years and are associated with the early civilisations of the Middle East and Asia.
In India, evidence has been found of simple stone-rubble structures for
impounding water that date back to the third millennium BC (Agarwal & Narain,
A Whole Life Costing Approach for Rainwater Harvesting Systems Richard Roebuck PhD, Bradford University
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1997). In the Negev desert in Israel, runoff from hillsides has been collected and
stored in cisterns to be used for agricultural and domestic purposes since
before 2000 BC (Evenari, 1961). There is evidence in the Mediterranean region
of a sophisticated rainwater collection and storage system at the Palace of
Knossos which is believed to have been in use as early as 1700 BC (Hasse,
1989). In Sardinia, from the 6th century BC onwards, many settlements collected
and used roof runoff as their main source of water (Crasta et al, 1982). Many
Roman villas and cities are known to have used rainwater as the primary source
of drinking water and for domestic purposes (Kovacs, 1979).
There is evidence of the past utilisation of harvested rainwater in many areas
around the world, including North Africa (Shata, 1982), Turkey (Ozis, 1982;
Hasse, 1989), east and southeast Asia (Prempridi & Chatuthasry, 1982), Japan,
China (Gould & Nissen-Peterson, 1999), the Indian sub-continent (Kolarkar et
al, 1980; Ray, 1983; Pakianathan, 1989), Pakistan and much of the Islamic
world (Pacey & Cullis, 1986), sub-Saharan Africa (Parker, 1973), Western
Europe (La Hire, 1742; Hare, 1900; Doody, 1980; Leggett et al, 2001a), North
and South America (McCallan, 1948; Bailey, 1959; Moysey & Mueller, 1962;
Gordillo et al, 1982; Gnadlinger, 1995), Australia (Kenyon, 1929) and the South
Pacific (Marjoram, 1987).
2.3 Rainwater harvesting in a modern context
During the twentieth century the use of rainwater harvesting techniques
declined around the world, partly due to the provision of large, centralised water
supply schemes such as dam building projects, groundwater development and
A Whole Life Costing Approach for Rainwater Harvesting Systems Richard Roebuck PhD, Bradford University
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piped distribution systems. However, in the last few decades there has been an
increasing interest in the use of harvested water (Gould & Nissen-Peterson,
1999) with an estimated 100,000,000 people worldwide currently utilising a
rainwater system of some description (Heggen, 2000).
2.3.1 Rainwater harvesting in the developed world
In the developed world the use of RWH to supply potable water is mostly limited
to rural locations, mainly because piping supplies from centralised water
treatment facilities to areas with low population densities is often uneconomic.
The development of appropriate groundwater resources can likewise be
impractical for cost reasons (Fewkes, 2006). Perrens (1982) estimates that in
Australia approximately one million people rely on rainwater as their primary
source of supply. The total number of Australians in both rural and urban
regions that rely on rainwater stored in tanks is believed to be about three
million (ABS, 1994). In the USA it is thought that there are over 200,000
rainwater cisterns in existence that provide supplies to small communities and
individual households (Lye, 1992). Harvesting rainwater for potable use also
occurs in rural areas of Canada and Bermuda (Fewkes, 2006).
The use of RWH systems to supply non-potable water to buildings in urban
areas has increased in popularity in the last 15-20 years (Fewkes, 2006).
Examples of non-potable end uses include WC flushing (Fewkes, 1999a; Bray
& Grant, 2002), urinal flushing (Cooper, 2001; Environment Agency, 2005a),
laundry cleaning (washing machines) (Ratcliffe, 2002), hot water systems
(Coombes et al, 2000c), garden/landscape irrigation (Weiner, 2003; Devi et al,
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2005), car washing (Leggett et al, 2001b) and fire-fighting (Gould & Nissen-
Peterson, 1999). Systems have been installed in a wide range of building types
including domestic properties (Leggett et al, 2001b; Day, 2002; Coombes et al,
2003a), high rise buildings (Thomas, 1998; Lau et al, 2005), schools (Bray,
2003; Paul & Bray, 2004), offices (Brewer et al, 2001), sports stadiums (Gould,
1999a; Environment Agency, 2003a), garden centres (Stephenson, 2002),
airports (Appan, 1993) and exhibition centres such as the Millennium Dome in
London (Hills et al, 1999; Lodge, 2000; Smith et al, 2000; Hills et al, 2002) and
the Eden Project in Cornwall (CIWEM, 2007).
The number of RWH systems installed varies from country to country. For
instance, in Germany during the 1990‟s the market leader alone installed over
100,000 systems, providing a total storage volume in excess of 600,000m3
(Herman & Schimda, 1999). It has been estimated that between 50,000 and
100,000 professionally designed systems are currently installed in Germany
each year (Konig, 2001; Environment Agency, 2004) and the total number of
built systems is believed to be approximately 600,000 (Leggett et al, 2001b). By
comparison, France has few installed systems. Those that do exist are often
simple, inefficient and used mainly for garden irrigation, with the domestic
utilisation of rainwater for flushing toilets and washing machines being virtually
non-existent. This low uptake is attributed primarily to the organisation of the
French water supply system which is essentially a set of regional monopolies
that have no incentive to introduce rainwater harvesting techniques since it
would reduce their profits (Konig, 2001).
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In urban locations, rainwater catchment surfaces tend to be restricted to roofs
(Hassell, 2005; Fewkes, 2006) although runoff can also be collected from other
impermeable areas such as pavements, roads and car parks. Runoff from these
areas can be more polluted than that from roof surfaces and may require a
higher degree of treatment to achieve an acceptable level of water quality
(Leggett et al, 2001b; Martin, 2001). Water storage and distribution elements
generally consist of standardised pre-manufactured components that can range
from a simple water butt with a tap at the base to more complicated systems
that can consist of underground storage tanks, filters, UV units, pumps and
automated controls. Where the latter type of arrangement is concerned, the use
of package (proprietary) systems dominates the UK market and it is possible to
purchase a complete system from a single supplier. One supplier stated that the
overwhelming majority of their domestic sales were of the proprietary type as
were most of those for commercial, institutional and industrial applications,
though bespoke systems could be designed if required (Nick Bentley of
Envireau Ltd, personal communication, June 2005).
Konig (2001) states that in the past components such as tanks, pumps and
filters were often supplied in kit form and had to be assembled on site,
necessitating the use of skilled staff and leading to increases in both installation
times and costs. Modern systems tend to be „modularised‟ and consist of
standardised mass-produced components, usually of high quality. Components
such as tanks, pumps and filters are delivered to site as complete units (no
assembly required), are easier to install and commission than the older types of
system and offer a greater degree of design flexibility. Some suppliers sell
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storage tanks with integrated filters, pump and electronic controls in what is
essentially a complete system that only requires connecting to the relevant on-
site pipework and power points.
With regards to water storage, the most common approach is to use
underground tanks (Hassell, 2005) although storage in other structures is also
possible, e.g. in the gravel sub-base of permeable driveways and pavements
(Pratt, 1995; Pratt, 1999; Leggett et al, 2001b) as well as above-ground tanks
and ponds (Woods-Ballard et al, 2007).
2.3.2 Water use in domestic, commercial and institutional buildings
The average per capita consumption for households (both metered and
unmetered) in England and Wales is currently around 150 litres per person per
day (Ofwat, 2006a). Figure 2.2 shows the water consumption share of different
micro-components in a typical UK domestic household (POST, 2000). The
diagram shows that not all of the water used in a household needs to be of
potable quality, particularly water used for WC flushing (31%), washing machine
(20%) and outside supply (4%). Potentially, about 55% of the potable mains
water used within a typical UK household could be replaced with another source
such as rainwater, provided that it was of a suitable quality for the intended
uses.
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Figure 2.2 Water consumption by micro-component for a typical UK
household (Adapted from POST, 2000).
Water usage patterns are different in office buildings compared to domestic
dwellings. WC and urinal flushing are often major consumers of water and can
account for up to 63% of water use, as shown in figure 2.3. As with domestic
properties, there is no specific need for this water to be potable and it could
potentially be substituted with rainwater provided that an adequate quality at the
point of use was achieved.
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Figure 2.3 Average water use in office buildings
Adapted from Leggett et al (2001a), p23.
2.3.3 Common drivers for RWH in the developed world
Most developed countries rely heavily on centralised water treatment and piped
distribution systems in order to provide a safe and reliable supply to the public.
Jeffrey & Gearey (2006) state that modern consumers have come to expect a
„right‟ to clean water, with infrastructure developments focusing on meeting
consumer demand with little restraint on quantity or quality. This has led to the
development of water delivery systems that supply excess water at excess
quality for the uses to which much of it is put, e.g. using potable water for toilet
flushing and garden watering. Increases in demand are typically met by further
resource development (Howarth, 2006). For instance by the construction of new
reservoirs, enlargement of existing ones and/or the development of further
groundwater resources (Lallana et al, 2001). However, in some countries this
approach has begun to present a number of difficulties. For example, Germany
relies to a large extent on groundwater for its public water supply which has led
to over-extraction, lowering of the water table and adverse environmental
A Whole Life Costing Approach for Rainwater Harvesting Systems Richard Roebuck PhD, Bradford University
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effects. Pollution of groundwater resources is also becoming a potential public
health risk (Sayers, 1999). Hiessl et al (2001) questions whether the continued
reliance on the centralised treatment and supply paradigm is the optimal choice
given the substantial operating/maintenance costs involved and increasingly
stringent environmental legislation.
The use of RWH systems in Germany has in recent years been promoted as
part of the solution to addressing these problems, with many city councils
providing incentives and subsidies to encourage their installation (Herrmann &
Schmida, 1999). Konig (2001) documents the use of RWH in a wide variety of
building types in Germany. Other potential benefits include the (so far
theoretical) ability to offset the development of new water resources (Schilling &
Mantoglou, 1999), reduce peak flow volumes and lower the risk of urban
flooding from the predominantly combined sewer system (Vaes & Berlamont,
2001).
In Sweden, increasing urbanisation and the widespread use of large-scale
centralised treatment has resulted in a supply system that is vulnerable to
shortages and has also contributed to water quality deterioration. Research has
indicated that demand management measures, including RWH for non-potable
uses, could help to reduce the amount of water required from the public supply
system for urban developments (Villarreal & Dixon, 2005).
In Australia there is a move towards Integrated Urban Watershed Management
(Mitchell, 2004; Roon, 2006), also known as Water Sensitive Urban Design
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(WSUD) (Argue et al, 2003). This approach involves considering the urban
water cycle as an holistic whole rather than as distinct separate entities (i.e.
stormwater, floodwater, wastewater and sources of potable water) with one of
the goals being to harvest and reuse stormwater in order to augment the mains
supply (Argue, 2001). Research has indicated that, as well as lowering reliance
on mains water, RWH has the potential to reduce the volume of stormwater
disposed of to the sewer system, reduce peak runoff rates (Coombes et al,
2001) and be economically viable at both the development and regional scales
(Coombes et al, 2000a, b).
Buildings that contain a water meter and in which the owners/occupiers are
charged for the water they use on a volumetric basis may be able to reduce
their water bills through the installation of a RWH system (Shaffer et al, 2004).
Whether or not this is a cost effective option depends on a number of factors,
including the capital cost of the RWH system, operation/maintenance expenses,
the volume of mains water that can be supplanted by harvested water and the
assumed lifetime of the system (Leggett et al, 2001b).
Rainwater harvesting may also have a role to play in promoting sustainable
urban water management. The EU Water Framework Directive (WFD), which
came into force in all member states in December 2000, calls for a range of
measures to be taken in order to protect the aquatic environment (EC, 2000).
The primary objectives of the WFD include a requirement to:
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Prevent further deterioration, and protect and enhance the status of
aquatic ecosystems, with regards to their water needs, terrestrial
ecosystems and wetlands (Article 1(a)).
Promote the sustainable use of water based on long-term protection of
available water resources (Article 1(b)).
Contribute to mitigating the effects of floods and droughts (Chave, 2001).
The literature suggests that RWH is potentially able to contribute towards the
achievement of each of these goals in a number of ways: by reducing reliance
on centralised water treatment and distribution systems that appropriate water
from the natural environment; lessening instances of urban flooding by reducing
both the volumes of water disposed of to the sewer system and peak flow rates
within sewers; by providing a water supply “buffer” in times of drought. Similarly,
other EU Directives have objectives that RWH could help to meet. For example,
the EU Habitats Directive (EC, 1994) requires that sites of European
conservation interest achieve favourable conditions by 2010. To achieve these
aims water abstractions in some areas may need to be reduced to a more
sustainable level (Environment Agency, 2005b), leading to increased pressure
on remaining supply sources. It is conceivable that the wider uptake of RWH
and similar technologies could to some extent mitigate the effects of reducing
permissible abstraction levels.
The rest of this review focuses on the types of rainwater harvesting systems
used in urbanised areas of the developed world for non-potable applications.
Systems suitable for use in domestic, commercial, institutional, public and
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industrial buildings for applications such as WC and urinal flushing, washing
machines and outdoor use (e.g. garden/landscape irrigation, vehicle washing)
are discussed but not industry-specific applications such as process or cooling
water. Particular attention is given to the use of proprietary („package‟ or „off-
the-shelf‟) RWH systems within the UK as these currently dominate the market
for urban installations in this country. The use of water butts is not considered
as these have limited potential for curbing reliance on mains water, peak flow
reduction or for reducing the volume of stormwater discharged to the sewer
system (Woods-Ballard et al, 2007). Relevant UK legislation and regulations are
discussed were appropriate. This information should not be assumed to apply
outside of this country.
2.4 Types and configurations of RWH systems
Three basic types of system for supplying non-potable water to buildings for
internal and external uses are identified by Leggett et al (2001b): directly
pumped, indirectly pumped and gravity fed. A number of variations are given by
Herrmann & Schmida (1999) and Konig (2001). External use only systems are
also available and these are essentially direct systems that can only be used for
outdoor purposes, such as garden watering and vehicle washing. In all cases,
water is collected from a catchment surface and held in a sealed storage
structure until needed. Once harvested water has been used, for example to
flush the WC, it is considered to be in the same effluent category as potable
water would be if used for the same purpose, e.g. harvested water used to flush
a WC becomes foul (black) water, the same classification that applies to potable
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water once it has been used to flush a WC. The resulting effluent is treated in
the same manner regardless of the initial source.
2.4.1 Indirectly pumped systems
Rainwater is initially held in a storage tank and then pumped to a header tank
within the building, which is usually located within the roof void. Water is
delivered to appliances via gravity and the header tank should be at least one
metre above the supply points. If the storage tank runs dry, the header tank is
supplied with top-up water from the mains. If the storage tank is full, any
additional incoming water will exit via an overflow and will normally be disposed
of either to a soakaway/infiltration device or sewer. See figure 2.4 for a
schematic of an indirectly pumped RWH system.
The main advantages of indirectly pumped systems are that if the pump fails
(e.g. due to mechanical/electrical failure or power loss) then water will still be
supplied to the associated fixtures and fittings via the mains top-up function.
Low cost pumps and simple controls are possible and systems tend to be
energy efficient as the pump runs at full flow (Environment Agency, 2007).
The main disadvantages are that they tend to deliver water at low pressures.
This can lead to slow filling of WC cisterns and the system may not provide
enough pressure to work with some appliances. Some proprietary units solve
the low pressure problem by using a hybrid system. Water for the WC is gravity
fed from a header tank which also has mains top-up whilst water for the
washing machine and garden is delivered via a pump at equivalent mains
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pressure. The advantage with this arrangement is that in the event of a power
failure it is still possible to flush the toilet. Indirect systems also require the use
of a header tank (Environment Agency, 2007). These can add to the overall
cost of a system (though not usually significantly) and there may not always be
sufficient space in the roof void to site the tank (Hannah Reid of Stormsaver Ltd,
personal communication, June 2007).
Figure 2.4 Schematic of an indirectly pumped RWH system
Adapted from Leggett et al (2001b), p38.
External use
Mains top-up
Overflow
Soakaway/infiltration device or sewer
Collection guttering
Cross flow filter
Rainfall
Storage tank
Pump
Supply
Overflow
Header tank
Key
Usable water
Discarded water
Manhole cover
Grey/black water to foul sewer system
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2.4.2 Directly pumped systems
In a directly pumped system (sometimes also referred to as a pressurised
system) rainwater is initially held in a storage tank and then pumped directly to
the point of use when required, e.g. to WC cisterns and washing machines.
There is no header tank with a direct system and mains top-up occurs within the
storage tank. Mains top-up does not completely fill the tank but maintains a
minimum level that is able to meet short-term demand. If the storage tank is full,
any additional incoming water will exit via an overflow and will normally be
disposed of either to a soakaway/infiltration device or sewer. Figure 2.5 shows a
schematic of a directly pumped RWH system.
The main advantages of directly pumped systems are that water is provided at
mains pressure which is ideal for garden hoses and washing machines, and
that they do not require a header tank (Environment Agency, 2007).
The main disadvantages are that if the pump fails (e.g. due to
mechanical/electrical failure or power loss) then no water can be supplied. WCs
would have to be flushed manually (e.g. using a bucket of water) and washing
machines would not function. Mains top-up controls can also be more
complicated than with indirect and gravity fed systems (Environment Agency,
2007).
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Figure 2.5 Schematic of a directly pumped RWH system
Adapted from Leggett et al (2001b), p38.
2.4.3 Gravity fed systems
Gravity fed systems differ from the direct and indirect variants primarily in that
the main storage tank is located within the roof void of the building. Rainwater is
collected from the roof, filtered and then piped directly to the storage (header)
tank. Water is delivered to appliances via gravity and the storage tank should be
at least one metre above the supply points. Mains top-up water is supplied
directly to the tank if it runs dry. If the tank is full, any additional incoming water
will exit via an overflow and will normally be disposed of either to a
soakaway/infiltration device or sewer.
External use
Soakaway/infiltration device or sewer
Collection guttering
Cross flow filter
Rainfall
Storage tank
Pump
Supply
Overflow
Mains top-up
Key
Usable water
Discarded water
Manhole cover
Grey/black water to foul sewer system
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The main advantages of gravity fed systems are that they do not require a
pump or electrical supply as is the case with the direct and indirect versions
(Fewkes, 2006). Also, since there is no pump, there is no risk of pump-
associated supply failure.
The main disadvantages are that the water pressure is likely to be less than that
of the mains supply. This can result in poor performance of some appliances,
e.g. slow filling of WC cisterns, and some appliances such as some modern
washing machines may stop working altogether. In this case a pump may be
required to boost the water pressure (Leggett et al, 2001b). There may also be
issues with high structural loads, damage from leaking components and water
quality issues due to fluctuating temperatures in the stored water (Fewkes,
2006). It also has to be possible to collect runoff from the roof, filter it and
deliver it to the tank under the action of gravity. In this case the relative levels of
the various components (roof, filter and tank) are critical and it may not be
possible to find an arrangement that functions hydraulically (Fewkes, 1989).
See figure 2.6 for a schematic of a gravity fed RWH system.
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Figure 2.6 Schematic of a gravity fed RWH system
Adapted from Leggett et al (2001b), p39.
2.4.4 Selection of system type for domestic and commercial applications
Direct systems are usually recommended for use in domestic properties since
there is not always sufficient space in the building‟s roof void for the header tank
that indirect and gravity systems require. Also, direct systems have been found
to be better at providing the required flow rate of water (Hannah Reid of
Stormsaver Ltd, personal communication, June 2007). For commercial
situations, indirect (header tank) systems are generally recommended. One of
the primary reasons is that peak demands can be relatively high compared with
domestic situations. Consequently, if a direct system was used then the pump
may not be able to supply the required water at a sufficient rate, resulting in low
External use
Mains top-up
Overflow
Soakaway/infiltration device or sewer
Collection guttering
Cross flow filter
Rainfall
Supply
Tank
Key
Usable water
Discarded water
Grey/black water to foul sewer system
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flow and low pressure at the points of use. The header tank also acts as a
failsafe in the event of pump failure as water can still be supplied via gravity to
the WCs and urinals. This enables the premises to remain open in the event of
pump failure. Header tanks also ease demand on the pump, enabling units to
be used that operate at lower flow rates. This increases pump reliability and life
expectancy (Hannah Reid of Stormsaver Ltd, personal communication, June
2007).
2.5 Components of RWH systems
Proprietary systems can consist of a number of different components, some
specific to the RWH aspects and some which are part of the building but are
utilised as part of the rainwater system (auxiliary components). A list of typical
RWH-specific components could include some or all of the following items:
First-flush diverters.
Filters.
Storage device, e.g. tank.
Overflow arrangement (including backflow prevention device).
Pump and associated components.
UV unit.
Electronic controls/management systems.
Header tank (for indirect and gravity fed systems).
Mains top-up arrangement.
Distribution pipework.
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A list of auxiliary components could include some or all of the following items:
Guttering and collection pipework.
Catchment area, e.g. roof.
Figure 2.7 shows a range of common rainwater harvesting and auxiliary
components and demonstrates how they can be integrated in order to create a
complete system. The diagram shows an indirect system with a header tank but
most of the components could equally apply to a direct system as well.
Figure 2.7 Schematic showing range of common RWH system
components
Mains top-up with type AA/AB air gap
Overflow Collection guttering
Coarse filter
Storage tank
Pump
Non-potable supply
Overflow
First flush diverter
Soakaway/infiltration device or sewer
Soakaway/ infiltration device
or sewer
Catchment area
In-line filter(s)
Backflow prevention device
Electronic controls
UV unit
Potable (mains) water supply
Water meter
Potable supply
Header tank
In-tank filter
Key
Usable water
Discarded water
Solenoid valve
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2.5.1 First flush diverters
During dry periods roofs become contaminated with a variety of pollutants such
as atmospheric particulates, bird droppings, leaves and other debris (Cunliffe,
1998; Fewkes, 2006). When it rains, some of the contaminants are washed off
the catchment surface and transported in the runoff flow. The rainfall intensity
and number of dry days preceding a rainfall event significantly affects the
quality of the runoff, with long dry periods resulting in higher pollutant loads for a
given catchment (Gould & Nissen-Peterson,1999).
Research has shown that the initial „first flush‟ of runoff is more polluted than
subsequent flows and that the concentration of contaminants associated with a
given rainfall event tend to reduce exponentially with time. Therefore, diverting
the initial portion of runoff generated by a storm away from the storage device
will mean that the quality of water entering storage is improved and the need for
subsequent treatment reduced or even eliminated altogether (Wu et al, 2003;
Martinson & Thomas, 2005).
As a rule of thumb, for each millimetre of first flush collected the contaminate
load will be about half the amount present in the previous millimetre (Martinson
& Thomas, 2005). Figure 2.8 shows sketches of a range of commonly used first
flush diverter types. All involve the diversion and temporary storage of the initial
portion of runoff. The „interceptor‟ and „splitter‟ variants rely on filling a container
with the first flush and slowly releasing it via a throttled outflow. The majority of
subsequent runoff from the catchment surface bypasses the first flush container
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and is routed into the tank. The „pit‟ variant works on a similar principle except
that outflow from the first flush container is into the ground via infiltration.
Gould & Nissen-Peterson (1999) state that the use of first flush diverters tends
to be limited and when they are used they often suffer from a lack of
maintenance. As a result of this neglect many function incorrectly or have
simply been disconnected by the building occupiers. Research conducted by
Coombes (2002) implies that the use of first flush diverters is fairly common in
Australia. However, Konig (2000) suggests that collecting the initial flush of
water is unnecessary for non-potable applications. Herrmann & Schmida (1999)
make no mention of diverters when discussing treatment processes for roof
runoff intended for non-potable uses in Germany. Mustow et al (1997) state that
the inclusion of such a device can increase the costs and complexity of a
system without providing any significant benefit. Limited evidence was found for
the use of first flush diverters in the UK and none of the proprietary system
suppliers provide them as a standard part of their package systems.
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Figure 2.8 Cross-sectional sketches of typical first flush diverters
2.5.2 Filters
It is recommended that rainwater be filtered before entry into the storage tank in
order to remove debris such as leaves, grit, moss and soil. Leggett et al (2001b)
identify a range of filter types and sub-types. Filters should be easy to clean (or
self-cleansing) and should not block easily (Martinson & Thomas, 2003). With
regards to contemporary systems, the use of crossflow filters is essentially
ubiquitous and these are described in more detail below. Cartridge filters are
First flush splitter (Adapted from Che et al, 2003)
Outflow
Inflow
Throttled first flush outlet
Container for holding
first flush
First flush interceptor (Adapted from Ntale, 2003)
Inflow Outflow
Throttled first flush outlet
Container for holding
first flush
Buoyant sphere, creates watertight seal when container is full
Outflow Inflow
Debris screen Concrete baffle
First flush passes through holes in base of box into infiltration chamber
Reinforced concrete box
First flush infiltrates into ground
First flush pit (Adapted from Coombes, 2002)
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often employed in systems that have a UV unit. These are also discussed
further.
Crossflow filters
Crossflow filters contain a mesh screen which water flows across (hence the
name) and that separates the flow into two fractions. The portion that passes
through the mesh is cleaned of all debris larger than the mesh size (typically
0.2-1.0mm) and passes to the storage tank. The residual debris is washed from
the mesh by the remaining fraction of water and diverted away from the tank,
e.g. to the sewer system or an infiltration device. Crossflow filters are
considered to be self-cleansing since debris is automatically washed from the
mesh screen.
Figure 2.10 shows two types of commonly installed crossflow filter
configurations. One is a downpipe filter in which the mesh sits adjacent to the
pipe wall. Water running down a vertical pipe at atmospheric pressure mostly
flows down the inside wall and downpipe filters take advantage of this
phenomenon by intercepting the flow and filtering the majority of it. Vortex filters
(which are usually located underground) use the momentum of the incoming
flow to create a vortex effect, swirling the water around the inside of the filter
casing which is lined with a fine mesh. Water is forced through the mesh,
filtering out debris and sending the processed water to the storage tank. As with
the downpipe version, the unfiltered water and associated debris are diverted
away from the tank.
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Figure 2.9 Cross-sectional sketches of typical crossflow filters
German best practice recommends the use of filters with porosities in the range
of 0.2-1.0mm with no further filtration required for non-potable uses (Konig,
2001). Self-cleansing filters are preferred as they require less maintenance and
reduce the cost of consumables (Leggett et al, 2001b).
Filter casing
Downpipe crossflow filter (Adapted from Leggett et al, 2001b)
Downpipe
Filter mesh
Filtered water to tank
Debris and unfiltered water
Filtered water to tank
Incoming water
Debris and unfiltered water
Filter casing
Vortex action
Filter mesh
Vortex crossflow filter (Adapted from Leggett et al, 2001b)
Incoming water
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Cartridge filters
Cartridge filters are usually placed after the storage tank and require that water
be passed through them under pressure. They are most often used in systems
that require a high degree of water quality and low turbidity, such as those that
include a UV unit or for potable applications. It is common practice to have
several arranged in series with the unit that has the largest porosity first in line
and subsequent units arranged according to diminishing pore size, e.g. 25μm
followed by 5μm. Cartridge filters tend to have small porosities and so pre-
filtration is required, for example by the prior use of a screen or crossflow
device. If this is not done then they will rapidly clog. They are not self-cleansing
and so require replacement at regular intervals, typically every 3 months or
thereabouts (Leggett et al, 2001b).
Other types of filter
Leggett et al (2001b) also describe a number of other filter types including in-
tank floating, screen, slow sand, rapid gravity, reed beds, membrane and
activated carbon. Chemical disinfection is also mentioned as another option for
improving water quality. Way & Thomas (2005) describe an experimental
system in which a slow sand filter was integrated into the actual rainwater tank.
However, with the exception of in-tank floating filters, none of these methods
would appear to have achieved any significant degree of penetration in the UK
market and none of the RWH system suppliers offered them as part of their
regular package deals. Therefore they are not discussed further in this thesis.
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2.5.3 Rainwater storage devices
A storage device is required to collect and hold catchment runoff because
rainfall events occur more erratically than system demand (Fewkes, 2006).
Water storage capacity is required in order to balance out the difference
between supply and demand (Gould & Nissen-Peterson, 1999). In the
developed world the most commonly used storage device is the underground
tank (Hassell, 2005). Other types of reservoir structures exist, such as above
ground tanks and ponds (Woods-Ballard et al, 2007), the gravel sub-base of
permeable driveways and pavements (Pratt, 1995; Pratt, 1999; Leggett et al,
2001b), covered flat roofs (Mustow et al, 1997), the void space beneath
garages (Courier, 2002; Jones, 2002), geo-cellular structures (Stephenson,
2002) and small local aquifers (Argue et al, 1998; Coombes et al, 2000c;
Gardner et al, 2001). However, the use of storage devices other than
underground tanks appears to be limited in the UK, particularly within the
domestic market and so these alternative approaches are not considered
further.
Installing tanks underground has a number of advantages: it helps to prevent
algal growth by shielding the tank from daylight (Konig, 2001), protects the tank
from extreme weather conditions at the surface such as freezing spells (Leggett
et al, 2001b) and helps to regulate the water temperature in the tank, keeping it
cool and limiting bacterial growth (Fewkes & Tarran, 1992).
Storage tanks come in a variety of shapes and sizes and can be constructed
from a range of materials including concrete, ferrocement, bricks, steel and
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plastics such as glass reinforced plastic (GRP) or high-density polyethylene
(Leggett et al, 2001b; Fewkes, 2006). Some are relatively basic in design whilst
others are essentially complete systems that incorporate the tank, filters, pump
and mains top-up arrangement in a single integrated unit. Tanks for domestic
systems generally have storage volumes in the 1-10m3 range. Tanks for
commercial systems are available in a wider range of sizes and can be tens or
hundreds of cubic metres in size. Vessels can also be linked together to provide
additional volume meaning that there is no theoretical upper limit on the amount
of storage space that can be provided, site constraints not withstanding. Figure
2.10 shows examples of the types of underground tanks that are available.
For a given tank the purchase and installation costs are related to the storage
capacity (Fewkes, 1997) and so it is important to select a tank with an
appropriate volume. There is a balance between cost and performance which
has to be judged carefully. Determining the optimum tank volume is a key
aspect of this thesis and is covered in more detail in chapters five, six and
seven. Whichever tank is selected, current best practice recommends that it
should be sized such that it overflows at least twice per year in order to facilitate
the removal of any floating debris (Fewkes, 2006).
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Figure 2.10 Examples of underground storage tanks
2.5.4 Storage device overflow arrangement
Modern rainwater tanks have an overflow arrangement in order to prevent
localised flooding if the capacity of the tank is exceeded, and also to help avoid
stagnation of stored water and remove floating debris. The overflow can be
connected to a soakaway/infiltration device, storm drain or combined sewer
system but not a foul sewer (Leggett et al, 2001b). It must include an anti-
backflow device in order to prevent contaminated water entering the tank in the
Moulded plastic tank (Courtesy of Freewater UK)
Ground level
Sectional concrete tank (Adapted from Leggett et al, 2001b)
Sealed joints to ensure tank
integrity
Lockable manhole cover
Sectional concrete rings
Inflow
Integrated tank system (Courtesy of Rainharvesting Systems Ltd)
Inflow
Filtered flow
Overflow
Ground level
Complete concrete tank (Adapted from Konig, 2001)
Filter screen (basket)
Lockable manhole cover
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event of downstream surcharging (DCLG, 2006a, part 1.70b). Overflows are
predominantly unrestricted (no throttle) and water passes through them via
gravity flow although pumped overflows are also available.
2.5.5 Pumps
RWH systems require that stored rainwater be pumped either to the point of use
(direct systems) or to a header tank located at least 1m above the point of use
(indirect systems). In general, gravity fed systems do not require a pump since
water is fed straight from the catchment surface to a high-level storage tank.
However, they are sometimes used with gravity systems in order to increase the
water pressure which may otherwise be too low to work with certain appliances,
e.g. some modern washing machines.
Pumps have a finite lifespan and will require repair/replacement at some point,
typically after 5-10 years of use. It is also recommended that they are checked
at least once per year in order to ensure that they are functioning correctly
(Leggett et al, 2001a).
2.5.6 UV units
Ultraviolet (UV) radiation is effective at killing a wide range of waterborne
bacteria and viruses. UV disinfection has a number of advantages: ease of use,
requires no chemicals, short retention time, no effect on the chemical
characteristics, taste or odour of the water, maintenance is not onerous, and
there is no risk from excessive use as might be the case with chemical
treatments (McGhee, 1991). UV disinfection of potable water supplies has been
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shown to be sufficient for the inactivation of 99.9% of most microorganisms
(Hall et al, 1997).
UV units can be fitted to RWH systems in order to safeguard water quality.
However, in order for a UV unit to effectively kill microorganisms the water has
to have a low turbidity, necessitating the use of fine filters (e.g. a 25μm filter
followed by a 5μm filter, located in series before the UV unit). If this is not done,
suspended solids in the water can effectively shield harmful pathogens from UV
light and they may not be destroyed (Crittenden et al, 2005; Parsons &
Jefferson, 2006). The use of a UV unit will add to the capital and running costs
of a system. Extra filters are required and these need replacing every six
months or so. The UV bulb consumes electricity and also has a finite lifespan,
generally requiring replacement after about six months of use (Leggett et al,
2001b; Shaffer et al, 2004). UV units fitted to RWH systems tend to be passive,
i.e. they do not control the rate of flow through them. Rather, the capacity of the
pump should be matched to the treatment flow rate of the UV unit.
In the normal mode of operation, the UV unit is left permanently on as
constantly switching it on and off as demand dictated would significantly shorten
the life of the bulb. Power consumption for domestic units is typically in the 15-
55W range and lamps generally last for between 8,000-10,000 hours of
continuous use (Crittenden et al, 2005), which equates to about twelve months.
Prolonged use can reduce the UV output intensity and so it is recommended
that lamps be replaced after a maximum of 10,000 hours even if they are still
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functional (Krishna et al, 2005). Figure 2.11 shows a schematic of a typical UV
disinfection unit.
Figure 2.11 Schematic of a UV disinfection unit
Adapted from Leggett et al (2001b), p52.
In the UK there is currently no legal requirement for a RWH system to
incorporate a UV unit and the literature did not provide any definitive guidance
on when and where one should be used. One supplier stated that UV
disinfection is not necessary and was primarily introduced into the UK market in
order to reduce the perceived risks associated with harvested water, thereby
encouraging its use (Glyn Hyett of 3P Technik, personal communication, 22nd
April 2006). Another stated that they would only recommend UV treatment in
special cases and that coarsely filtered rainwater was of sufficient quality for
toilet flushing and irrigation purposes and did not normally require further
treatment (Lutz Johnen of Aqua-Lity, personal communication, 24th April 2006).
Water in
Irradiated water out
Control panel
UV lamp
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2.5.7 Electronic control and management units
Many contemporary RWH systems have the option of including an electronic
control and management unit. This is not essential and some systems can be
controlled using simple mechanical float valves and a low-level switch to trigger
the pump. However, more sophisticated controls allow for the use of float
switches, pressure sensors and electrically actuated valves which can result in
better overall performance (Leggett et al, 2001b). Controls can also have visual
readouts of systems status, such as the level of water in the tank, or report if
there is a problem such as pump failure, disinfection failure or filter blockage
(Konig, 2001). A significant fraction of the proprietary systems currently for sale
in the UK come supplied with electronic controls as standard.
Electronic controls consume electricity and so will add to system running costs,
although power consumption is generally low. They also have a finite lifespan
and will likely need replacement after 15-20 years (Lutz Johnen of Aqua-Lity,
personal communication, 24th April 2006)
2.5.8 Header tank
Indirect systems require the use of a header tank. This is normally located in the
roof void of the building and should be at least 1m above the point of supply.
High and low level switches are used to signal the storage tank pump when to
activate and when to disengage. If mains top-up occurs in the header tank then
this is usually controlled by a low level switch in conjunction with a solenoid or
float valve (Leggett et al, 2001b).
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2.5.9 Mains top-up arrangement
Given the intermittent nature of rainfall it is rare that a RWH system can be
designed such that a constant supply of harvested water can be guaranteed. In
times of shortfall it is advisable to have a top-up arrangement which can supply
enough mains water to meet short-term demand. Top-up can be provided in a
number of locations. In an indirect system it most commonly occurs in the
header tank, although it can also be in the storage tank. Direct systems
normally have mains top-up in the storage tank although a variation exists
known as a “centralised” system in which the pump and mains top-up are
integrated into a single unit located inside the building. If the main storage tank
runs empty, mains water is fed into the suction pipe of the pump and from there
water is transferred directly to the point of use (Woods-Ballard et al, 2007). Top-
up controls can consist of simple mechanical valves controlled by flotation
devices or more complicated systems involving float activated switches coupled
with solenoid valves.
2.5.10 Solenoid valves
Solenoid valves are typically used to start/stop the mains top-up function. A float
activated switch, located either in the header tank (for indirect and gravity fed
systems) or primary storage tank (for direct systems), triggers the valve if the
water volume falls below a predetermined level. This activates the mains top-up
function, ensuring that a minimum amount of water is available at all times.
Once the minimum water level has been restored, the float activated switch
closes the valve, shutting off the flow of mains top-up water.
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Solenoid valves have a typical life expectancy of between 5 and 10 years
(Leggett et al, 2001a). The power consumption of solenoid valves suitable for
use in RWH systems is low, typically in the range of 2-5W and they only
consume power when operating (Jerry Cook of Red Dragon Valves Ltd,
personal communication, 25th May 2007) so running costs can be expected to
be minimal.
2.5.11 Distribution pipework
A pipe distribution network is required to transport water from the storage tank
to the point of use and a wide selection of pipes are available that are suitable
for this task. Further information on appropriate pipe materials and installation
protocols can be found in The Water Supply (Water Fittings) Regulations 1999
(HMSO, 1999), WRAS (1999a) and Leggett et al (2001b). Plastic pipes are
commonly used. These are durable and, if installed correctly, have a long
service life although they will require replacement at some point, typically after
about 20 years of use (Leggett et al, 2001a).
2.5.12 Guttering and collection pipework
Rainwater runoff from the catchment surface needs to be collected and diverted
to the rainwater storage device. If the catchment surface is a roof then collection
is generally via a system of gutters feeding into one or more downpipes and
from there into the storage device. For further information refer to HMSO (1999,
2000a) and WRAS (1999a).
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2.5.13 Catchment surface
In urban locations the most commonly utilised catchment areas are roofs
(Hassell, 2005; Fewkes, 2006) although runoff can also be collected from other
impermeable areas such as pavements, roads and car parks (Environment
Agency, 1999a). Not all of the rain falling on a catchment area can be collected
as some is lost from the system due to processes such as depression storage
and evaporation (Wilson, 1990; Butler & Davies, 2004). Other factors that also
influence the amount of lost water include the rainfall depth and intensity,
antecedent conditions, the material the catchment is made from and the
catchment slope (Li et al, 2004).
The effective runoff is the volume of rainwater falling on the catchment that can
be collected and routed into the collection network of gutters and pipes. When
estimating the effective runoff volume, a commonly used approach is to employ
a dimensionless runoff coefficient that represents the observed losses from the
catchment compared with an idealised catchment from which no losses occur
(Fewkes, 2006). The effective runoff is calculated by multiplying the volume of
rain falling on the roof by the coefficient. A coefficient value of 0 would mean
that no runoff occurs whilst a value of 1 would mean that all the rain falling on
the catchment is translated into effective runoff. Examples of runoff coefficients
for a variety of different roof types are given in Leggett et al (2001b) and are
reproduced below in table 2.1. This data is based on the long-term experience
of German RWH system manufacturers
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Table 2.1 Common roof runoff coefficients
Adapted from Leggett et al (2001b), p42.
Surface Type Coefficient
Roof Pitched roof tiles 0.75-0.90 Flat roof, smooth surface 0.50 Flat roof with gravel layer or thin turf (<150mm) 0.40-0.50
2.6 Water quality
In the UK, for harvested water intended for potable uses the Private Water
Supplies Regulations (1991) apply (Leggett et al, 2001a). By contrast, there are
currently no legally binding quality criteria for water derived from reuse systems
(rainwater and greywater) intended for non-potable uses (Roaf, 2006). Kim et al
(2007) state that in order for water systems to become more sustainable the
quality of the water supplied should correspond to the intended applications.
This practice will help to identify alternative sources that can be utilised where
demand is for non-potable water. The same principle has also been proposed
by a number of other authors, e.g. Alegre et al (2004); Sakellari et al (2005).
The information presented thus far in this chapter has demonstrated that
rainwater can be used for a number of non-potable applications such as WC
flushing, washing machines, garden irrigation and vehicle washing. None of
these uses involve the (intentional) consumption of harvested water. It could
therefore be argued that standards less stringent than those required for
potable water would be acceptable for non-potable uses such as these.
In the UK a range of water quality guidelines and recommendations exist for
rainwater harvesting systems. Some of these are derived from monitoring
studies conducted on RWH systems, such as those monitored as part of the
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„Buildings That Save Water Project‟ (Brewer et al, 2001). Others are based on
existing standards such as the European Union (EU) Bathing Water Directive
and World Health Organisation (WHO) recommendations. Mustow et al (1997)
recommend that quality guidelines should be application specific and propose
different „categories of use‟, each with different quality requirements depending
on the likely degree of human exposure. Leggett et al (2001b) state that the
greatest risk of microbiological contamination occurs when water is ingested or
deliberately sprayed, creating an aerosol. Thus uses such as surface crop
irrigation and vehicle washing would require a higher level of water quality than,
for example, subsurface irrigation and toilet flushing. A sample of
recommendations found in the literature that relate to non-potable uses are
summarised in table 2.2. Most of the information relates to microbiological
quality since this is often considered to be the criteria of most concern when
dealing with water reuse systems (WROCS, 2000).
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Table 2.2 Summary of recommended microbiological water quality
standards for non-potable applications
Reference
Uses
Key indicators
Threshold values
WHO (1989) Irrigation of crops likely to be eaten uncooked, sports fields, public parks
Faecal coliform per 100ml
≤1000
Irrigation of public lawns with which the public may come into contact, e.g. hotel lawns
Faecal coliform per 100ml
≤200
Leggett et al (2001b)
Washing machines Total coliforms per 100ml E.coli per 100ml
0, or counts less than 10/100ml acceptable providing not in consecutive samples 0
WRAS (1999a) Toilet flushing Faecal coliform per 100ml Faecal enterocci per 100ml
<10,000 <100
EC Bathing Water Quality Directive (76/160/EEC)
Toilet flushing Total coliforms per 100ml Faecal coliform per 100ml
<10,000 <2,000
Most non-potable use guidelines are less strict than those applicable to potable
water supplies and allow for the presence of some bacteriological organisms.
WRAS (1999a) make the point that most people are exposed to literally millions
of faecal organisms whilst performing everyday activities and that for harvested
water to add to the burden of exposure the faecal coliform content would need
to be in excess of 10,000 per 100ml. Leggett et al (2001b) state that where
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rainwater from a catchment with low contamination is used for WC flushing,
washing machines and irrigation, and the system is well designed and operated,
then disinfection is not necessary and should not be applied. For single-user
installations (which includes domestic systems serving only one property) that
are intended for WC flushing, irrigation and other non-potable uses Shaffer et al
(2004) consider that coarse filtration and settlement provide satisfactory
treatment. For multi-user installations (commercial and domestic systems
serving several properties) the same criteria are recommended with the addition
that disinfection to achieve a total coliform count <1,000 colony forming units
(cfu) per 100ml should be applied if thought to be necessary. The United States
Environmental Protection Agency (USEPA, 1992) and WHO (1989) guidelines
also allow for some degree of microbiological contamination as does the EU
Bathing Water Directive (76/160/EEC). Konig (2001) states that in well designed
and operated systems only coarse filtration prior to entry into the storage tank is
required and that the risk to human health from non-potable applications is
minimal.
In light of the above information it was decided that water quality would not be
explicitly considered in the thesis. It was assumed that adequate quality can be
maintained for non-potable uses providing that, in line with the previous
recommendations, rainwater undergoes coarse filtration prior to entry into the
storage tank. The use of UV sterilisation may be considered in some instances
but for domestic situations it was assumed that the use of UV is not necessary.
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2.7 Contemporary rainwater harvesting in the UK
Compared to countries such as Germany the UK lags behind in the application
of RWH technology and it has been estimated that by the turn of the millennium
only between 1,000 and 2,000 systems had been commissioned (Hassell, 2001;
Leggett et al, 2001b). However, the market is growing and at the time of writing
it is reported that approximately 400 systems per year are being installed
(UKRHA, 2007). The majority of system sales in the UK currently originate from
member companies of the UK Rainwater Harvesting Association (UKRHA). This
organisation is a focus group established in 2004 in order to help coordinate the
activities of the private sector, disseminate information about and promote
RWH, liaise with the Government and also contribute towards the research and
development of RWH technology. They currently have 14 full members and it is
believed that these represent about 75% of the UK market, which at the end of
2006 was estimated to be worth over three million pounds (Terry Nash of
Freerain™, personal communication, February 12th 2007).
2.7.1 Barriers to the uptake of RWH systems
Roaf (2006) discusses the barriers for water conservation and reuse in the UK
from the perspective of a range of stakeholders and actors, including central
government & regulators, local authorities, water companies, private
consultants, architects, developers & planners, manufacturers, and customers &
consumers. The key points raised that are of relevance to rainwater harvesting
systems have been summarised in table 2.3. A more detailed discussion can be
found in Roaf (2006), pages 221-233.
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Table 2.3 Summary of key barriers to the uptake of RWH systems in UK
Adapted from Roaf (2006), pp221-233.
Stakeholder(s) Key barriers
Central Government and regulators
Lack of water quality standards; lack of empirical data on which to base quantitative risk models; unwillingness of any Government or regulatory body to take responsibility for setting and monitoring standards
Local authorities Lack of knowledge by managers, council members, planners, building control officers and environmental health officers; poor communication between departments, lack of information regarding RWH system costs, maintenance requirements and water quality standards
Water companies Profit motive for investing in water efficiency measures is low; industry focus is on reducing consumer costs not on creation of a sustainable water supply system; water sector in general lacks imagination, prefers single product mindset (mains supply) rather than multi-product mindset of which RWH could be a part
Private consultants
Water efficiency currently seen as a poor relation to energy efficiency in terms of earning potential; lack of good quality information on the economics of water conservation and reuse; lack of clear standards; lack of a developed market for associated products
Architects, developers and planners
General lack of knowledge and awareness; additional costs of construction and maintenance associated with water conservation and reuse systems; lack of current water quality standards; lack of a common technical language with which engineers, planners and architects can discuss water related systems
Manufacturers Difficulty in achieving and maintaining reliable level of water quality; no established water quality standards; lack of an established market for water related products; uncertainty surrounding expected service life of systems; pioneering status of much of the technology; lack of good quality research with which to inform technology development
Customers and consumers
UK does not have an established culture of water conservation; consumers tend to be reactive in their habits; low availability of good quality information; current low value of mains water; aversion to what may be seen as „experimental‟ technology; water quality issues
A number of other researchers have investigated or considered barriers to
uptake. These are summarised in table 2.4.
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Table 2.4 Further barriers to the uptake of RWH systems in UK
Reference Identified barriers
Brewer et al (2001); Leggett et al (2001a,b)
Unproven cost benefit, difficulties in operation and maintenance, lack of water quality standards and associated public health concerns, unproven technology and lack of guidance
Grant (2006) Cost effectiveness of systems, particularly domestic, is questionable
Woods-Ballard et al (2007)
Potential risk to public health, possible expense and complexity of installation, above ground tanks can be unsightly
Brown et al (2005) Cost of water rarely a driver for the end-user but cost of installing a RWH system may be seen as significant
2.7.2 Public perception and acceptability
One of the key factors in the success or otherwise of any water reuse scheme is
the perception of the users and the acceptability to them of the existing or
proposed technology. It is important that the social and cultural aspects of water
use are considered when planning and designing such systems (Jeffrey &
Gearey, 2006). Past failure to adequately take into account and address public
concerns has led to the cancellation of a number of potentially beneficial reuse
schemes (DeSena, 1999).
A review of the relevant literature was undertaken and the main results are
summarised in table 2.5. The information presented in this table shows that
there is little public opposition against, and some considerable support for, the
use of harvested water for non-potable applications such as toilet flushing,
laundry washing and garden irrigation. Generally speaking, the less personal or
intimate the use, the higher the level of acceptability. The assumption is
therefore that the use of RWH systems for non-potable applications, such as
those considered in this thesis, would not be hampered in any significant way
by opposition from the general public.
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Table 2.5 Summary of key findings relating to the public perception
and acceptability of non-potable RWH systems
Reference(s) Key findings
WPCF, 1989; WROCS, 2000; Hills et al, 2003; Lazarova, 2003
Toilet flushing generally most readily accepted use for recycled water. Acceptability found to decline as use becomes more „personal‟, i.e. as direct human contact becomes more likely
Bruvold, 1985 Uses such as WC flushing are preferred to more intimate uses such as food preparation and cooking
Brewer et al, 2001 Little concern reported over use of harvested water for WC flushing
McDaniels et al, 2000
Aesthetics (e.g. colour, odour and turbidity) impact upon the willingness to use recycled water, although these indicators may not necessarily be a reliable guide to actual water quality
Jeffrey, 2002; Jeffrey & Gearey, 2006
People are generally more accepting of the use of recycled water in their own homes than they are in public or institutional buildings
Leggett et al, 2001b If RWH systems are to become successful in the domestic market then their reliability will need to be comparable to that of other domestic systems such as hot water appliances
Hills et al, 1999, 2002
Investigation into performance and public perception of a combined greywater, rainwater and groundwater system at the UK Millennium Dome. Out of >1,000 users interviewed, 95% agreed that such systems were appropriate for use in public areas
BMRB, 2006 Telephone survey in which 473 UK homeowners were asked various questions regarding their water use habits and opinion of RWH systems. 92% agreed that RWH was “a good idea” and 30% stated that they would be more likely to buy a house if it had a RWH system already installed. 63% stated that they would be most likely to install a system for financial reasons (e.g. reduced water bills)
2.7.3 Drivers and potential benefits of RWH systems
In the UK as elsewhere there is an emerging consensus that the traditional
centralised and disparate approach to the urban water cycle is neither optimal
nor sustainable (Argue, 2001; Hiessl et al, 2001; Maheepala et al, 2003, 2004;
Anderson, 2005; Sakellari et al, 2005; Stacey, 2005; Roon, 2006). Historically,
the primary aim has been the promotion of economic growth and the urban
water cycle has essentially been compartmentalised with water supply, storm
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drainage and wastewater treated as separate entities. This approach has led to
the overexploitation of water resources and environmental damage (Geiger,
1995). Pratt (1995) identifies a range of problems currently facing the UK water
sector:
1. In some parts of the country water demand is exceeding the available
supply.
2. Resources that are available are not always located in areas of demand.
This can result in the distribution of water over large distances (Fewkes,
2006).
3. Low flows in rivers due to over-abstraction.
4. Increased capital investment in water reclamation works has not always
led to a corresponding improvement in receiving water quality.
5. The expansion of urban areas has resulted in increased runoff volumes
and peak flow rates, negatively impacting river geomorphology, aquatic
habitats and water quality.
6. Traditional approaches to flood alleviation can themselves create further
problems elsewhere.
Shaffer et al (2004) list a number of drivers for sustainable water management:
climate change, demographic changes, potential reduction of surface runoff and
urban pollution, potential to save costs and planning requirements such as the
need to comply with Planning Policy Statement (PPS) 25: Development and
Flood Risk (DCLG, 2006a) and the Building Regulations Part H: Drainage and
Waste Disposal (DCLG, 2006b). Roaf (2006) also provides a similar list of
drivers: climate change, demographics, increasing rates of per capita
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consumption, increasing rates of groundwater extraction, freshwater reserve
depletion, increasing concentrations of chemical and organic pollutants in rivers
and lakes, and increasing public opposition as well as practical barriers to major
new dam projects.
The search for alternatives to the traditional solutions to urban water
management are by no means limited to rainwater harvesting systems. There is
on-going paradigm shift occurring in the UK towards the application of more
sustainable and holistic approaches. Some of these measures include, but are
not limited to:
The use of SUDS for urban drainage (Martin, 2001; Wilson et al, 2004;
Woods-Ballard et al, 2007).
Demand management measures (Butler & Memon, 2006).
Increased metering of domestic properties (Roaf, 2006).
Voluntary codes of practice for improved water efficiency in new homes
(e.g. DCLG, 2006c) and other buildings (e.g. BREEAM, 2007).
Proposed changes to the regulatory framework and Building Regulations
(House of Lords Select Committee, 2006).
Improved leakage management strategies (Trow & Farley, 2006).
Financial incentives such as the Enhanced Capital Allowance (ECA)
scheme for water efficient technologies (HM Revenue & Customs,
2007a)
Research projects (e.g. Balmforth, 2005).
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Existing legislation that places water companies under a Duty to promote
water conservation to customers, such as the Environment Act 1995
(Roaf, 2006).
New legislation such as the Water Framework Directive (EC, 2000;
Sakellari et al, 2005).
Rainwater harvesting for non-potable uses in urban areas primarily resides in
the „demand management‟ category as the primary objective is to reduce the
volume of mains water used. If RWH systems can reduce reliance on the public
water supply then arguably there is good reason to believe that they can
contribute towards the new sustainable urban water management paradigm.
There are also a range of other potential benefits such as reducing the risk of
urban flooding, financial savings and helping to offset the need to develop
further resources (Leggett et al, 2001a). In some locations the provision of RWH
systems may be a condition for planning agreements (Elliott et al, 2005). One
RWH system supplier stated that about 15% of their domestic sales were
influenced by planning requirements and that this figure would grow
substantially in the future once the Code for Sustainable Homes (DCLG, 2006c)
was transposed into the Building Regulations (Terry Nash of Freerain™,
personal communication, 23rd April 2007). Leggett et al (2001a) provide a
comprehensive summary of the potential benefits of rainwater harvesting and
this is reproduced in table 2.6.
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Table 2.6 Potential benefits of RWH
Adapted from Leggett et al (2001a), pp28-29.
Benefit Stakeholder(s) who benefit Applicability and sensitivity
Reduction in the use of mains water (and potential financial savings)*
Customer in reduced mains water charges Water Supply Undertaker in reduced need for capital investment in water supply infrastructure
Will only have an effect with widespread uptake
Reduced impact on water resources (and potential to offset need to develop further resources)*
Society benefits in an improved natural environment
Will only have an effect with widespread uptake
Reduction in mains supply peak demand
Customer mains supply more assured
Will only have an effect with widespread uptake
Reduction in local flooding risk
Society and building owners
Will only have an effect in a local catchment. This could be significant for new developments
Reduction in stormwater overflow
Society benefits in an improved natural environment Sewerage undertakers in reducing Combined Sewer Overflow (CSO) operation
Will only have an effect with widespread uptake
Development of a new market both in the UK and overseas
Suppliers and manufacturers UK economy
The UK market is likely to develop slowly over the next 10 years (from 2001) but there are clear opportunities in overseas markets such as Germany, South Africa and Australia
Contribution to sustainability
Society, environment, economy
Needs to be reviewed on an individual basis to ensure local sustainability. Sustainability of water resources in the UK will not be affected unless there is widespread uptake
Green public relations Individual organisations, building owners or occupiers
Benefits are being realised even from small projects. This can support corporate or organisational ideals and be used to demonstrate what is possible
Continued on next page
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Table 2.6 continued…
Criteria for development permission
Developers Local Environment Building purchasers
Rainwater on individual development scale enabling development to proceed
Independence from mains water supply
Consumer Requires space and money to meet water needs. Likely to be applied in only a few cases
*Text in italics added by the author
There is a degree of supporting evidence originating from a number of other
countries for some of these benefits, e.g. Schilling & Mantoglou (1999);
Coombes et al (2000a, 2001); Vaes & Berlamont (2001); Coombes & Kuczera
(2003a); Villarreal & Dixon (2005); MJA (2007). However, there are limited
corresponding studies specific to the UK. Some research does exist, such as
that produced by CIRIA and a handful of case studies from the Environment
Agency Water Efficiency Awards, and various university researchers have
published peer-reviewed work. However, there are many claims for the
supposed benefits of RWH that appear to have little substantive evidence to
support them.
For example, Woods-Ballard et al (2007) state that rainwater harvesting has the
advantage of reducing both peak flow rates and discharge volumes, ranking the
performance of both of these indicators as “high” but no evidence or references
are provided with which to corroborate these claims. Similarly, Hassell (2005)
states that “once a rainwater harvesting system is installed, rainwater from the
site is diverted before it adds to the load on the stormwater drainage”. But how
much water can be expected to be retained, and under what circumstances?
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Again there is no evidence or references provided with which to check this
claim. Some suppliers state that a domestic system can save a typical
household up to 50% of its water needs. However, claims such as these often
appear to be based on an implicit assumption that a system is capable of
meeting all non-potable requirements rather than any empirical analysis which
would indicate that this is achievable in all but a small number of cases, e.g.
Day (2002).
The following sub-sections examine the recognised potential benefits of RWH
systems that are relevant to this thesis. That is, the potential reduction in mains
water use by substituting it for harvested water in non-potable applications. Key
evidence from the literature which is relevant to the UK is highlighted in order to
determine the legitimacy of the claimed benefits that RWH can bring.
Preference was given to studies that included an empirical element rather than
purely theoretical/academic research since the goal was to ascertain actual
measured, not speculative, benefits. Work that merely alluded to potential
benefits and did not provide any supporting evidence or reasoned thinking was
not included.
2.7.4 Reduction in mains water use (and potential financial savings)
A reduction in mains water use is frequently cited in the literature as one of the
primary benefits of installing a RWH system, e.g. see Gould & Nissen-Peterson
(1999); Konig (2001); Leggett et al (2001a,b); Fewkes (2006). For buildings that
contain a water meter, and are therefore charged for mains supply on a
volumetric use basis, there is also the possibility of financial savings since some
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amount of mains water can be replaced by harvested rainwater, resulting in a
reduction in the user‟s water bills. Harvested water should not be considered a
„free‟ resource however as any RWH system has its own associated costs
which have to be balanced against any reduction in mains supply charges.
Whether or not a RWH system can result in an overall financial saving depends
upon a number of site-specific factors, such as RWH system capital, operation
and maintenance costs, local climatic conditions, catchment type and area,
water demand, mains water and sewerage charges and so forth. The
economics of RWH are an important part of this thesis and are covered in more
detail in later chapters. This section in only concerned with reporting the general
results of work done by others in order to assess in broad terms the likely levels
of reduction in mains water use, and whether or not financial savings are
possible.
A small number of UK studies exist in which the amount of mains water
substituted by harvested rainwater was monitored in-situ, with some level of
volumetric water savings observed in each case. The financial benefits were
generally less clear cut, with claims that some systems provided an overall
(often small) financial saving whilst others resulted in an overall financial loss.
For the sake of brevity only the key findings from a selection of cases are
presented here, in tables 2.7-2.9.
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Table 2.7 Key RWH water saving and financial results for the ‘Buildings
That Save Water’ project (Brewer et al, 2001)
RWH system description
Key water saving and financial results
Office building with 50 occupants and 1,500m2 roof area. Indirect RWH system used to supply water to 12 WC‟s and 4 urinals. System included coarse filtration followed by a string filter and a UV unit. Building also incorporated low flush toilets and urinal controls
Annual water usage for WC‟s and urinals was 376m3/yr, of which 150m3 (40%) was supplied by the RWH system. Reduction in annual water bill estimated as £241/yr. RWH system capital costs were £7,250 (purchase and installation). Yearly operating and maintenance costs were £214/yr, yielding a net saving of £27/yr. Payback period estimated as 267 years
Office building/ecological builders merchant located in a newly refurbished 3-storey warehouse with 275m2 roof area. Occupancy was 10 staff, plus visitors. Direct RWH system used to supply 6 WC‟s, 4 urinals and 4 utility sinks used for cleaning purposes
Annual water usage for WC‟s and sinks was 53m3/yr, of which 34m3 (64%) was supplied by the RWH system. Reduction in annual water bill estimated as £40/yr. RWH system capital costs were £3,200 (purchase and installation). Yearly operating and maintenance costs were £27/yr, yielding a net saving of £13/yr. Payback period estimated as 240 years
Ecological housing development consisting of 5 „sustainable‟ terraced houses. All houses self-sufficient in water, no connection to mains supply. Rainwater for non-potable uses collected from roads, an earth banking behind the houses and surrounding grassland was filtered and used to supply water to 5 baths, 10 toilets and 10 taps
Annual non-potable consumption was 377m3/yr, all of which was supplied by the RWH system. Total reduction in annual water bills for all 5 houses estimated as £512/yr (compared to equivalent mains supply). RWH system capital costs were £11,854 (purchase and installation). Yearly operating costs were £110/yr, yielding a net saving of £402/yr. Payback period estimated as 30 years
Notes: financial calculations were basic and did not include the use of a discount rate or irregular maintenance fees such as pump repair/replacement. Inclusion of these factors would have made the systems even less financially efficient. For primary reference, see Brewer et al (2001). See also: Leggett et al (2001a,b).
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Table 2.8 Key RWH water saving and financial results for the
Environment Agency water efficiency awards
Reference RWH system description Key results
Environment Agency, 2001b
Humberstone golf course: existing underground storage chamber adapted for use as part of RWH system for irrigation
Annual water use for irrigation was 4,700m3/yr, of which 1,400m3 (30%) was supplied by the RWH system. Few financial details available, payback estimated at approximately 5 years
Environment Agency, 2003a
Alfred McAlpine sports stadium: water collected from north stand, sports/office complex and selected hard surfaces. Water filtered, UV treated and used for pitch irrigation Great Oak domestic dwelling: 4-bed house with indirect domestic RWH system used to supply WC, basement tap and 2 outside taps Christchurch junior school: indirect system collecting water from 1,100m2 roof used to supply 27 WC‟s, 4 urinals and 2 external taps Denys E Head Ltd: system using a surface pond for storage used to provide irrigation water to garden centre plant nursery.
Annual water savings of 3,119m3/yr reported. No financial details available Annual water savings of 100m3/yr reported. No financial details available Water usage estimated as 876 litres/pupil/yr compared to 3,790 litres/pupil/yr for a similar building, indicating a 77% reduction in water usage. No financial details available Capital costs were £4,000. During first year of operation, system displaced 6,700m3 of mains water, saving over £4,000
Environment Agency, 2005a
Beaumont primary school: rainwater collected from roof and used for WC and urinal flushing as well as garden irrigation Belvedere House: flagship head office of engineering consultancy FaberMaunsell fitted with various water saving devices including a RWH system Sutton Courtenay Environmental Education centre: RWH system for supplying water to low-flush WC‟s to visitors centre with over 5,000 visitors per year
During first year of operation, 170m3 of water was used for aforementioned purposes, of which 63m3 (37%) was supplied from the RWH system. No financial details were available RWH system estimated to have provided 25% of total water use within the building. No financial details available Monitoring showed that RWH system was able to supply 49% of the centres water needs. No financial details were available
Note: no discount rate used in any of the above cases
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Table 2.9 Key water saving and financial results from a number of
domestic RWH system case studies
Reference
RWH system description
Key water saving and financial results
Ratcliffe, 2002
3-bed household in Telford with RWH system supplying water for WC flushing
Water usage for WC flushing estimated at 165 litres/day of which (on average) the RWH system was able to supply 110 litres/day (22% of total household demand). System capital costs were £2,500. No further financial details were available
Day, 2002 RWH system installed at the Millennium Green development, Newark. 24 new homes were fitted with RWH systems for WC flushing, washing machines and outside taps
Results for house on “plot 7”: total water demand over the monitoring period of 248 days was 75.7m3, of which 35.6m3 (47%) was supplied by harvested rainwater. No financial details were available
Stephenson, 2002
Harvesting/irrigation system installed at a garden centre, Gonerby Moor. Runoff collected from 3,000m2 roof area and used to irrigate 15,000m2 plant display area
No figures available but between 2002-2004 mains water only required for relatively brief period after prolonged period of dry weather. Would indicate significant water savings. No financial data available
Fewkes, 1999a
RWH system installed in 2-bed single storey domestic property in Nottingham. Harvested water used to flush two 9-litre WC‟s
Over 12 month monitoring period 63.8m3 was used to flush WC‟s of which 36.4m3 (57%) was harvested rainwater. No financial details were given in this particular paper
2.7.5 Reduction in mains water use: discussion
The evidence presented above illustrates that RWH systems are able to reduce
reliance on the public water supply by substituting mains water with harvested
rainwater for various non-potable end uses, with WC flushing been the most
common. The case studies reviewed indicated that up to ≈50% of non-potable
domestic demand can be met with harvested water but that in practice a wide
range of system performances can be expected. Little data was available with
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regards to the financial performance and in some cases no financial
assessment was made at all.
Systems installed in commercial and institutional buildings were most commonly
used for WC and urinal flushing. Water saving efficiency varied significantly
between examples and it seems unlikely that generalisations can be made
regarding the performance of such systems. Financially, commercial and
institutional installations would appear to be more viable than the domestic
versions, principally because the former generally have larger roof/catchment
areas and so it is possible to capture a greater volume of water. Also, for a
given commercial/institutional building the level of demand will probably exceed
that found in domestic dwellings, meaning that the potential savings are likely to
be higher for the former building type. However, as with the domestic examples,
limited empirical data was available with which to corroborate these statements.
The application of discounting techniques (in order to take into account the
opportunity cost of capital) was not apparent in any instance, a major limitation
in the those examples that did attempt some form of financial assessment.
2.8 Policy, regulation and guidance
There is currently no formal UK Government policy on the operation of
rainwater systems either in the home or within a commercial/industrial setting.
However, numerous regulations affect system installation as well as use and
some, such as the Health and Safety at Work Act, are relevant even when
installation occurs in a private house. Shaffer et al (2004, pp27-35) provide a
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summary of a range of policy, regulation and guidance documents that may
apply to the installation and operation of RWH systems. The Water Regulations
Advisory Scheme (WRAS) gives advice on the Water Supply (Water Fittings)
Regulations 1999 in WRAS (1999a,b). Best practice guidance documents are
available from CIRIA as a result of the „Buildings That Save Water‟ project
(Brewer et al, 2001; Leggett et al, 2001a,b). Guidance on the operation and
maintenance of RWH systems as well as example maintenance agreement
documents are provided in Shaffer et al (2004).
2.9 RWH literature review: summary and scope for further work
This literature review has demonstrated that rainwater harvesting is an ancient
technology that has been used around the world for millennia and continues to
be widely used to this day. In developed countries potable RWH systems tend
to be restricted to rural areas. Urban installations are mainly used for non-
potable applications such as WC and urinal flushing, laundry cleaning (washing
machines) and for outdoor uses such as garden irrigation and vehicle washing.
RWH systems have been installed in a wide variety of property types including
domestic, commercial, institutional, public and industrial buildings. The use of
standardised pre-manufactured modular systems is now common practice.
These offer several advantages such as a high degree of design flexibility, ease
of installation, high levels of reliability and a supply of water at a quality
consistently good enough for most non-potable applications.
Regarding water quality, it was noted that many rural communities around the
world rely on harvested rainwater to supply most, if not all, of their domestic
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water needs including drinking supplies. There have been very few reports of
adverse health effects from drinking rainwater in rural areas. In industrial and
urban areas harvested rainwater often fails to meet drinking quality guidelines,
particularly with respect to microbial standards. However, monitoring studies
have shown that, providing systems are designed and operated correctly,
harvested rainwater usually meets with guidelines applicable to non-potable
uses such as the EU Bathing Water Directive and guidance provided by WHO
and WRAS. The conclusion of researchers in the field has generally been that
rainwater collected from building roofs that has undergone basic treatment
processes (primarily coarse filtration) poses little risk to public health if used for
purposes such as toilet flushing, laundry washing and garden irrigation.
Numerous barriers to the uptake of RWH systems exist. These chiefly relate to
the absence of legally binding water quality standards, lack of high quality
research, current low cost of mains water, water utilities focus on profit
generation and macro scale solutions, unproven benefits, low consumer
awareness, apathy and/or reluctance to conserve water and risk aversion to
new technology. However, despite these obstacles the increasing pressure on
existing water resources, coupled with the apparent unsustainability of the more
traditional supply-side solutions, means that demand management options such
as RWH are likely to play an increasing important role in supplying the UK‟s
future water needs. Currently the UK market for RWH systems is small
compared to some other developed countries but appears to have significant
potential for growth.
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The potential benefits of RWH systems were identified. These included
reductions in metered mains water use and associated financial savings, as well
as reduced pressure on water resources and reductions in peak demand, local
flood risk and stormwater overflows. However, it needs to be recognised that
many of these benefits remain unproven within a UK context, with only a
reduction in mains water use having any reasonable volume of supporting
empirical evidence. Further work needs to be done in order to determine the
magnitude of the other possible advantages, if indeed they exist at all.
The remainder of this thesis focuses on the potential water saving and financial
benefits of RWH systems for new-build developments, particularly with regards
to the financial performance and viability of domestic installations. The scope of
the investigations was set at the single building scale as this can be considered
to be the basic „unit‟ for RWH system operation. Results generated at this level
could also be used in future studies concerning RWH system implementation at
the development and regional scales, which currently also lack good quality UK-
specific data.
Before any detailed research could be conducted it was first necessary to
determine the state of the art with regards to the design and financial
assessment of contemporary RWH systems. These aspects are examined in
the following two chapters.