Greywater Info

So what is greywater?Greywater! A few years ago this was a fairly uncommon term to most of us, but nowadays we can’tgo to the nursery or turn on the television without encountering greywater. But, what is it? How dowe use it? What effect will it have on my garden? Is it actually grey?

Greywater is technically household wastewater from the laundry (including the washing machineand tubs) and the bathroom (including showers, baths and basins). Toilet water and kitchenwastewater are regarded as blackwater and are not suitable for reuse in domestic gardens, due tothe potentially high levels of bacteria, fats and solids contained in this wastewater.

The diversion of greywater from the house and into the garden has become an extremely popularway of irrigating our precious green spaces in these times of low rainfall and water restrictions.When done correctly, it is an excellent way of saving water and money. It is amazing to think thatone average household (2.5 people) expels 124 100 litres of greywater a year! (fromwww.westernwater.vic.gov.au) That’s more water than most established gardens need in the sameperiod. And, unlike rainwater, greywater is available all year round, regardless of the weather!

But I’ve heard greywater use is bad for plants… is that true?Firstly, let me point out that research regarding the long-term impacts of greywater on plant andsoil health is seriously lacking, so the affects of usage are, at this stage, a bit of an unknownquantity. Also, the greywater we are discussing here is untreated greywater (that is, one that has notbeen modified or had it’s quality improved by an approved greywater treatment system).

Remember, the quality and performance of greywater irrigation can vary dramatically, dependant ona number of factors. These include

the type of greywater used (eg: washing machine vs. bathwater)■

the types of chemicals included in greywater (eg: soaps and washing powders)■

the irrigation method■

the type of plants being watered■

the length and duration of watering■

the soil structure and type■

the presence of soil organic matter and so on.■

That said, there are some straight forward ‘do’s, don’ts’ and ‘no-you-didn’t’ regarding greywater andthese have been popped together in an easy to use reference chart for you all.

Do consider a professionally installed, fail safe greywater treatment system – saves you time time,stress, effort and may make you eligible for a rebate

Do monitor your soil – check pH, smell, “life forms” eg worms, bugs etc.

Do monitor your irrigation needs – if it doesn’t need water, don’t water it!!!!!

Do disperse the water subsurface – either on top of soil and under mulch, or trenched into soil. It’sbetter for your plants, your health, and your back pocket (will avoid a big fat fine!).

Do allow your garden a rest from greywater – turn it off in autumn, and back on in spring!

Do think carefully about the products you use inside the house, and what affect that will haveoutside eg: disinfectants, hair dye, bleach, cleaners

Do restrict greywater use to your garden – untreated greywater is not suitable for washing cars,hosing down paths, washing windows etc.

Do filter out as many solids as you can.

Do get to know greywater rules and regulations – your local council, state water board and the EPAare great places to start

Don’t store untreated greywater for over 24hours – it’s against EPA regulations, it’s really bad foryou and it stinks!

Don’t water just because the greywater is there – you’ll drown your plants and your soil, so checkthe soil moisture levels first and then decide

Don’t water your vegie patch with greywater – for so many reasons, this is just plain wrong!

Don’t shandy greywater with rainwater in a tank or similar – you still can’t store it, and you run aserious risk of harbouring E. coli , among other things

Don’t allow pets or people to play in pooled greywater – that’s revolting!

Don’t hose it around… it can be really contaminated – always disperse your greywater under mulch,or in the soil (subsurface)

Don’t use kitchen water or water contaminated by pee or poo… this is fairly obvious

Don’t let greywater wash into your neighbours yard or neighbouring properties – nothing saysneighbourhood dispute like your waste water in the yard next door

What can I actually water with greywater?There has been a huge increase in the use of native and indigenous plants in domestic gardens andwhy wouldn’t there be? They look great, are suited to local soils and conditions, create habitat forour precious native animal species and can be a lot more aridity tolerant than many exotic species.But the use of greywater on these types of gardens can be a bit of a mystery and has caused greatdebate among nursery folk and gardeners alike.

The four issues of most concern with regard to greywater and natives are:

· Phosphorus· High pH· Alkalinity· Salinity

Talking PhosphorusLet’s first take a look at phosphorus. Many commonly grown Australian native plants have originatedin phosphorus deficient soils and high levels of phosphorus can be detrimental to the health of theseplants. Phosphorus sensitivity is a particular issue with members of the Protea family (Proteaceae)which includes Banksia, Grevillea, Hakea and Isopogon. However, phosphorus sensitivity varies andit should not be assumed that all Australian native plants will not tolerate phosphorus.

With that in mind, it is always preferable to choose a detergent that contains low or no phosphorus ifyou are irrigating with greywater. This will avoid any detrimental affects to soil health and planthealth, both in your backyard and beyond the back fence (think blue-green algal blooms). To find outwhether your detergent has a high phosphorus content, check out the Lanfax Labs websitewww.lanfaxlabs.com.au, for detailed information on many different brands of washing detergents.

Low phosphorus detergents must be used in any long-term application of grey water from laundrysources, regardless of the phosphorous sensitivities of plants or not. Excessive phosphorus is unableto be taken up by plants, and has the potential to damage soil structure, as well as leaching into ourgroundwater, and polluting our rivers, creeks and bays.

pH and AlkalinityThe next issue we need to tackle is one of pH and alkalinity. Research has shown that even some ofthe best detergents for greywater use can be quite alkaline which, over time and with repeatedapplication, can alter the soil pH considerably. Want to learn more about the confusing world of pHand alkalinity… click here.

Generally speaking, laundry water is quite alkaline due to the detergents used, and this can, withapplication over prolonged periods, alter the pH of the soil, making conditions unpleasant for loadsof plants and for soil microbes (more on that later). Plant preferences for certain types of soil meansthat they are often starved of important nutrients or damaged by unwanted minerals when the pH isaltered.

The make up of laundry liquids and powders is complex, and relies on a myriad of differentchemicals and compounds to do its work. Laundry detergents need to be alkaline in order to“attract” grease, fats and all those yucky things that make us need to wash our clothes in the firstplace.

Laundry detergents also contain “surfactants”, substances which, when added to water, significantlyreduce the surface tension of the water, allowing water to wash surfaces better. There are manydifferent types of organic compounds which can function as surfactants, but, while they might getour clothes cleaner, they aren’t doing our soil, or the critters living in the soil, much good.

So, in basic terms, much laundry water has the potential to cause significant changes to soilstructure, soil pH, and, in turn, affect how our plants grow. Using detergents with a neutral pH (orclose to it) will help keep soil pH at a desirable level. If you are finding your greywater to bealkaline, adding white vinegar (which is slightly acid) to the greywater before applying it to the soilmay be beneficial for the long-term health of plants and soil. The amount of vinegar required willvary depending on the starting greywater pH, test it out for yourself!

Loads of native and exotic plant species do not tolerate an alkaline soil (most of our native soils inAustralia are quite acidic, SA being the exception) so monitoring of the soil pH over time isimportant. The magic word here is ‘test’ i.e. test your pH for yourself, and see where you stand.

pH testing kits are available from most garden centres, aquariam retailers and pet supply stores,and are specifically designed to test the pH, acidity and alkalinity of water (including greywater).Soil pH testing kits are also available, and are an essential addition to the garden shed!

I heard greywater is salty – is it?Salinity is mainly a problem with washing machine water as many powder detergents have a highsalt content due to the use of fillers in laundry powders. Preferably do not use saline greywater,

especially with clay soil types, unless your plants can tolerate it. You could add gypsum to the washwater if it is saline (i.e. high sodium concentration). Alternatively, using liquid detergents orchoosing powders with no sodium content are much safer and environmentally responsible options.

What do I do with all this water?The biggest issue faced by gardeners irrigating with untreated greywater is not necessarily thequality of the water, but the amount of it and frequency at which it is being applied. Put simply,people are watering more than they ever did and are literally drowning their plants and their soil.Please, for the love of the Garden Gods, check your soil moisture before irrigating. If the soil isdamp, direct your greywater to the sewer, rather than to the garden! Greywater cannot be stored forlonger than 24hours, so, if you don’t need it, divert it! Oh, and give your soil time to recover. All soilsunder greywater irrigation should be allowed freshwater and the best time for this is through winter,when rainwater is generally available. So turn off your greywater over autumn and winter, and flickit back on as the weather warms up and the rains stop!

What about the water from my bathroom?On average, a two to three person household generates 185 litres of greywater per day from thehand basin, shower and bath. The chemical constituents of bathroom greywater include soap,shampoo, hair dyes, toothpaste and cleaning chemicals. Greywater from hand basins is morepolluted than bath or shower greywater, but is much lower in volume. If hair dyes and cleaningchemicals are being utilised, divert the greywater to the wastewater rather than the garden.

I get asked quite often how the use of soaps and shampoos will impact the quality of greywater usedfor garden irrigation, and the short answer is “we don’t know”. Generally speaking, the amount ofsoap and shampoo used in the shower is quite minimal, and pretty well diluted by the time it getsout to the garden. Most of it is biodegradable, and is unlikely to have any significant long-termimpact on the plants and soil. That said, the impacts of all types of greywater are dependant on awhole host of factors, including soil types, organic matter content and so on.

What will greywater do to my soil?Hard to say really! As we have learnt, the use of greywater with a high content of laundry detergentcan be quite harmful to plants, causing phosphorus toxicity and sodium issues. But the truth is, we

don’t know at this stage what the long-term impact of greywater use on gardens will be. Thewidespread use of greywater for irrigation is a fairly new beast, and one that, until now, has notbeen studied a great deal. While there are numerous studies underway, the outcome on soil healthwill not be known for some time. But we can infer a few things at this stage:

· Harsh chemicals that are designed to kill household bugs are most likely to kill beneficial bugs inthe soil. This includes the use of eucalyptus oil, nappy soakers, antiseptic and anti-bacterial productsand carbolic acid based disinfectants.

· Petroleum based products such as some detergents and optical brighteners – they are slow to bio-degrade and probably not real good for the soil

Maintaining soil health by adding plenty of organic matter is essential (even more than usual) tocounteract the effects of any additional salt. It will also help to buffer the pH because anotherbenefit of adding lots of organic matter is that it can help lower pH, which in turns makes lessphosphorous available to plants. Check out the Soil Health section at the top of our website for moreinformation on the importance of healthy soils!

Greywater is great… an awesome resource that, when used correctly and cleverly, can prevent ourprecious potable drinking water from being dumped into garden beds.