Basics of Rain Water Harvesting

Rain Water Harvesting is a way to capture the rain water when it rains, store that water above ground or charge the underground and use it later. This happens naturally in open rural areas. But in congested, over-paved metropolitan cities, we need to create methods to capture the rain water.

A sample urban installation – Roof rainwater collection – in a metropolitan city

· If you live in a single dwelling house or a multi-tenant apartment complex, you already have 80% of the RWH system. We just need re-orient the plumbing design.

· The present design of the house will take all the rainwater from the roof and all the ground level areas surrounding the house and flow the water towards the street. (where it floods the street, clogs the storm drains and sewer lines for a few days, before flowing away as sewage water)

· From the roof tops, bring the rainwater down using closed PVC pipes and direct it to a sump. Include a simple 3-part filteration unit consisting of sand, brick jelly and broken mud bricks

· If you do not have sump, use a well. In many parts of the country, old wells when they go dry, is used as garbage dumps. Please clean the well and put the rain water into it.

· If you do not have a well, construct a baby well (about 2ft in diameter and about 16 feet deep based on soil structure)

· Other types of RWH – collect the ground water and stop their flow at the gate. Put a concrete slab with holes in it, build a 2 feet deep pit, across the full width of the gate. Collect and connect a pipe and flow the water to a well or a baby well.

Costs

All costs are subject to local variations in different parts of India. Use these figures for budgetary purposes only.

· Most often, the cost is from the PVC pipes. A 4″ diameter PVC pipe costs Rs xx per linear foot. A 5″ pipe costs lot more than a 4″ pipe.

· If you do not have a sump, include about Rs 5 per litre of water storage. So, a 10,000 litre size sump will cost Rs 50,000. (For a family of 4, using about 80 litres per day per person, this 10,000 litre size sump will contain 1 month’s water needs for this family.

· If you do not have old style well – 6′ to 8′ diameter and about 60 feet deep, it will cost about Rs 5,000.

If you wish to construct a baby well, it may cost around Rs 2,500

Benefits

· A water tanker bringing water from unknown sources and untested for its quality will cost about Rs 1000 to Rs 2500 for 10,000 litres of water.

· You cannot put a price on ‘peace of mind’ knowing that you have water for a month.

Did you know that..

· A well is not for storing water. The well connects the surface to the underground water sources. Based on the underground water availability during a rainy season, the water level in the well will go up and down.

· Long after the rains have stopped, the well gets its water from the underground sources leaking into it.

· Where you get water using a bore-well, rain water did percolate through any soil structure at the ground level, including rocky, laterite rock surface.

· Every bore well will eventually go dry, some sooner, some later.

· Use a bore well in reverse. Use a dried up bore well to recharge the underground supply by adding a percolation pit at the top

A sample rural installation – rain water collection – in a small village.

Recognize first that 3 positive aspects of a village as it relates to water harvesting.

1. The village population is about 500+ families or about 1,500+ residents.

2. Most villages don’t even have roads. There are no paved parking lots in a village.

3. A villager’s house is about 300 sq.feet – whether it is made of a thatched roof or a concrete roof. Even if you collect the rain water from the roof or from the sides, you often find kitchen waste water running in the middle of the street.

What types of RWH makes sense in the rural areas?

a. Build community wells in a few places in the village. Within 10-20 feet from the well, construct a bore-well using a hand-operated pump. Educate the villagers to keep the area around the well and the bore well clean – no washing (human, cattle, motor cycles, clothing), no defecation.

b. If there are existing water tanks in the village, desilt and dredge them every 3 years.

c. If there are any small rivers or streams, build check-dams across them to hold the rain water for usage after the rains have stopped.