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Rainwater
harvesting
Rainwater harvesting is the collection and storage of rain from roofs or a
surface catchments for future productive use. This method is
used in many parts of the world, where there is enough rain for collection and conventional
water resources either do not exist or are at risk of being over-used to supply
a large population. Rainwater harvesting can provide lifeline water for human
consumption. It helps to build reservoirs which may require the use of valuable land.
It has been estimated that the amount of rain water that falls on the terrace
of a house can take care of the water requirement of an average family of four
members for one year. Traditionally, rainwater harvesting has been
practiced in arid and semi-arid areas, and has provided drinking water, domestic water, water for livestock,
water for small irrigation and a way to replenish ground water levels. This
method may have been used extensively by the Indus Valley Civilization.
Rainwater harvesting in urban areas can have manifold reasons. To provide
supplemental water for the city's requirement, to increase soil moisture levels
for urban greenery, to increase the ground water table through artificial
recharge, to mitigate urban flooding and to improve the quality of groundwater
are some of the reasons why rainwater harvesting can be adopted in cities. In
urban areas of the developed world, at a household level, harvested rainwater
can be used for flushing toilets and washing laundry. Indeed in hard water areas.
It is superior to mains water for this. It can also be used for showering or
bathing. As rainwater may be contaminated, it is not suitable for drinking
without treatment. However, there are many examples of rainwater being used for
all purposes including drinking following suitable treatment. The rainfall pattern in India is highly irregular in space and time. Most of it
is concentrated during just a few months of the year and that too, in a few
regions - 70% of the rainfall occurs in about four months. So, even in a year of
normal rainfall, some parts of the country face severe drought.
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A Brief History of Water Harvesting in Our Country
India has had a tradition of
water harvesting which is more than two millenia old. Evidence of this tradition
has been found in ancient texts, inscriptions and archaeological remains. The
Kuhals of Jammu, Kuls of Himachal Pradesh, Guls of UttarKhand, Pats of
Maharashtra, Zings of Ladakh, Zabos of Nagaland, Eris of Tamilnadu, Keres of
Karnataka, Tankas, Kundis, Bawdis, Jhalaras, etc. of Rajasthan are but a few of
the traditional rain harvesting systems, which existed in India but now, dying a
slow death. Thar desert of Rajasthan provides a unique example of water harvesting system.
A rooftop water harvesting system is widely prevalent in Thar desert. Rain water that falls on the roof is taken through a pipe to an
underground tank known as kundi. A kachha structure known as
kui is dug next to the tank to collect the seepage. Since water is scarce, every drop must be preserved and used judiciously. At places people
bathe
on a stone block, from which water drains into an animal water
tank.
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Traditional Kundi in Rajasthan
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Rain water
harvesting method.
Rainwater harvesting is the collection of raindrops usually from a roof top.The rainwater collected from the roof flows through the gutters, into a collection tank. The size of the tank is dependant of the amount and purpose of the water but also of the annual rainfall and the size of
the roof. A normal sized tank for a roof of 20 to 40 square metres is 10 cubic
metres.
Required materials
A catchment area, usually a roof of 20 square metres or above is sufficient.
Roof-gutters, those can consist of bent metal sheets or even large split bamboo 'tubes'. Pipelines or gutters (bamboo, PVC, etc.) that lead from the
roof- gutters to the storage tank. A storage tank;
(between 5.000 and 12.000 litres) a concrete, a ferrocement or a
bamboo- cement structure is recommendable for relyability and sturdyness. Do mind that a man-hole should be present for
inside- cleaning purposes. The tank can be built both super- or sub-surface but consider that the outlet is situated at the bottom and must remain accessible. A vessel or a piece of garden-hose can be used to transport water from the storage tank to the slow sand filter. For the slow sand filter you need: a clean empty oil drum with a lid
some 500 litres large, clean (river) sand in different, separate granulities, ranging from medium coarse (2-4 mm) to very fine (20-100 um), partially perforated tubing (garden hose), a tap,
three clean stones of appr. 15 cm diametre and a flat stone or tile of
some 30 cm across .
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Rainwater
harvesting in rural areas
Rainwater harvesting in urban areas
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