Rainwater Harvesting In IndiaA rural and urban case study

S.Vishwanathwww.rainwaterclub.org

www.ircsa.orgwww.youtube.com/zenrainman

Photo : Norma Angelica Hernandez Bernal

In a water scarce world we need to conserve every drop of water

Rainwater harvesting

• Collecting and storing rainwater for future productive use. Storing can also be in aquifers through artificial recharge systems

• A rainwater harvesting system consists of catchment , conveyance, filtration and storage or recharge structure.

India- Policy recognition for rainwater harvesting

• The National Water Policy and the State Water Policy recognize the role of rainwater harvesting

• .. The efficiency of utilization of water will be improved and awareness about water as a scarce resource fostered. Rainwater harvesting and water conservation will be encouraged. Conservation consciousness will be promoted through education, regulation incentives and disincentives.

Source : http://waterresources.kar.nic.in/state_water_policy-2002.htm

Rural rainwater harvesting

• Rainwater from rooftops is collected in above the ground brick masonry tanks of 2000 litres capacity each in a 1000 villages

• Rainwater harvesting has been implemented in 23683 schools in rural Karnataka State

• In Fluoride affected areas more than 6000 underground rainwater tanks of capacity 5000-8000 litres each has been built through Government funding to provide water at 20 litres a year for the whole year.

A simple traditional rainwater harvesting system

An above the ground rainwater 2000 litre rainwater storage tank

Quality check- using the H2S vial test for e.coli identificationPut sample water in bottle and observe for 36 hours

Brown colour indicates no e-coli, black water would indicate e-coli

Simple treatment for e-coli in rainwater using SODIS

Keep water in a bottle for 5 hours in the sun www.sodis.ch

Rainwater harvesting in Bangalore city

• At the city level rainwater is collected in many lakes and allowed to infiltrate and recharge the groundwater

• At individual buildings, rainwater is harvested either by storing in sump tanks or by recharging through small wells.

Local hydrologic cycle – seeking bio mimicry with rainwater harvesting

Hydro-flows from a small plot

Before building After building

• Surface runoff 15 % 90%

• Recharge 10 % 5%

• Evapo-transpiration 75 % 5%

• The aim of rainwater harvesting is bio-mimicry. To restore the local hydrology on a plot as before building

A rain barrel is the simplest way to harvest rainwater

The new rainwater harvesting bye-law for Bangalore City

• For every plot create recharge or storage– @ 20 litres per square metre of roof area– @ 10 litres per square metre of paved area

Minimum depth of recharge well 3 metres

How to harvest rainwater ?

• Understand rain (quantum/pattern/intensity)

• Cascade capture

• House/Apartment/Institution/Industry/Park

• Storm water harvesting in ‘tanks’/lakes

• Ground water recharge

MONTH DAYS QUANTITY (mm)

JAN 0.2 2.70

FEB 0.5 7.20

MAR 0.4 4.40

APR 3.0 46.30

MAY 7.0 119.60

JUN 6.4 80.80

JUL 8.3 110.20

AUG 10.0 137.00

SEP 9.3 194.80

OCT 9.0 180.40

NOV 4.0 64.50

DEC 1.7 22.10

TOTAL 59.8 970.00

Rainfall pattern in Bangalore Maximum rainfall intensity 90 mm/hour

30 years data

EVERY ROOF IN A CITY CAN BE A CATCHMENT

Rainwater harvesting in an underground tank

A first rain separator and a sand filter

Harvested rainwater in underground tank

Site identification FOR RECHARGE with rainwater

The site should have a sufficient clean and large catchment. It should also permit fast infiltration and percolation.

Excavation

The excavation should reach porous soil / weathered rock / fracture.

Digging the pit

Back-filling. Round hard stones Smaller stones on top

Filling of the recharge pit with large stones first than small stones

Finished recharge pit with coarse sand filling over the small stones

Recharge pit around bore wells

The pit has reach the silt layer

Pit and concrete rings

Placing of the rings

The making of a recharge well – to put rooftop rainwater or stormwater into the aquifer. In Bangalore city, typically 6 metres deep and 1 metre diameter

Recharge wells details

Silt and leaves trap in a storm-water drainCovers : steel grill or perforated RCC

Rainwater going inside a recharge well

Re-charging a bore wellOutlet pipe in recharge well

Procedure• Locate recharge well in the storm water

channel or just off the channel

• Make arrangements to remove silt and leaves before water enters recharge well

• Monitor the rate of recharge and decide on the number of recharge wells necessary for the catchment

Don’t forget the maintenance

Recharge wells in storm-water drains

A landscaped recharge well in an office

We need rainwater harvesting for the Blue Planet Every drop counts