Rain water harvesting
If you reside in Bangalore, and have experienced water scarcity,
you might be searching for alternative ways to get enough
water for your household use. Prominent citizens of Bangalore
like S. Viswanath, founder of Rainwater Club
in the city and Yellappa Reddy, noted environmentalist
and former secretary of Karnataka Environment and Forest Department,
recommend harvesting rainwater to the people of the city facing
Harvesting rooftop rainwater is one answer to the city’s water
WHAT is rooftop rainwater harvesting?
The process of collecting, storing and using rain falling
on rooftops of houses or other constructions is called, rooftop
WHY harvest rainwater?
Because rainwater is a pure natural resource and saving it
makes ecological and financial sense.
WHO can harvest rooftop rainwater?
*Rainwater harvesting is for any person planning to build
a house or who is in the process of building a house on an
independent plot in Bangalore. Persons with already built
houses can also harvest rainwater by ‘retrofitting’ such a
built house for rainwater harvesting.
*Persons in apartments can also harvest rainwater but a community
approach may be required in such a case.
*Industries and factories can harvest rainwater since large
roof areas are usually available in such constructions.
*People who are purchasing water from private water tankers
can harvest rainwater to lessen their financial outflow.
WHEN to harvest rooftop rainwater?
It is possible to collect rainwater in Bangalore throughout
the year and use the same for gardening, car washing, washing
clothes, dishes, bathing, toilet, house swabbing and other
domestic non-potable purposes. If you want to use the harvested
rainwater for all purposes including drinking and cooking,
it is a must to boil and filter before use.
DESIGN your roof well for rainwater collection.
*A flat roof can be gently sloped to drain water towards the
storage system. *A ‘nahani trap’ or ‘floor trap' can be placed
at the time of casting the roof just near the inlets of the
down water pipes.
*Sloping roofs should have a gutter of PVC or Zinc sheet to
collect water and channel it to the down water pipe system.
*Roofs should be uncluttered and should be easy to clean by
sweeping and swabbing if necessary.
*Down water pipes should be designed well - 90 mm diameter.
PVC pipes resistant to UV rays appear to be the best bet as
down water pipes. Of course this depends on the roof area
to be drained.
*3 to 4 down water pipes seem enough for a 1,000 to 1,200
square feet area.
*Filter the rainwater before storage: Filtering can
be as basic as a floor trap placed before the water enters
the down water pipe or a piece of sponge placed at the inlet
of the down water pipe. A PVC bucket with gravel, sand and
charcoal is a good filter before rain water is stored. A PVC
drum with sponge on the inlet and outlet is also a filter.
A small two chamber inspection filter tank can also be devised.
DESIGN tips for rainwater harvesting.
Try to determine your storage system at the planning stage
itself. Would it be a:
* roof level storage tank
* a ground level drum or masonry tank
* a below the ground sump
*a partially below ground and partially above ground tank.
Locate the storage system appropriately.
* Roof level storage tanks may need to be at the rear of the
house or on the sides so that it is neither obstrusive or
* Ground level drums or tanks occupy space and should not
hinder movement or appear unsightly.
* Below the ground sump is a good option since most new constructions
in Bangalore go in for sumps anyway. Sumps are hidden from
view, less costly to build and do not obstruct movement.
Note: Always provide for an outlet for excess collection
of water from the storage system.
Further treatment of stored rainwater
* It is a common perception that water stored for long goes
bad. If water does not contain any organic material and if
it is stored in a clean container it can stay for very very
* Some small treatment like ‘alum dosing’ or ‘chlorination’
can also be done to stored water to improve its quality.
* Addition of a small quantity of alum dissolved in half a
bucket of water will bring down the suspended solids and clear
the stored rainwater.
* Similarly adding a small quantity of bleaching powder to
half a bucket of water and then mixing it with the stored
rainwater will kill bacterial contamination.
* Great care should be exercised while chlorinating and it
is not particularly recommended.
* It is always recommended that water used for drinking should
be boiled and filtered invariably.
Courtesy: Environment and Health Foundation (India).
The foundation, considering the severity of water scarcity
in Bangalore had conducted a seminar on ‘rain water harvesting
for Bangalore’ on November 11th, 1999, in the city.
For more tips on rain water harvesting contact EHF (India)
Address: # 7, 8th Main Road,
3rd Phase, 2nd Stage, Domlur,
Bangalore 560 071
Phone: 530 8137, 554 3397
web site: www.inika.com/chitra