Water management: rainwater harvesting and traditional water bodies
Rainwater harvesting collects and stores rain for later use or to recharge groundwater. Tamil Nadu's eris, ooranis and temple tanks are traditional ways of doing this.
Why manage water?
Only a small part of Earth's water is fresh and usable. Tamil Nadu gets the biggest share of its rain from the north-east monsoon (October to December). Rivers and wells dry up in summer. Groundwater falls when we pump too much. Water management means using, saving and storing water wisely, so there is enough for everyone all year.
Rooftop rainwater harvesting
- 1Rain falls on the roof, the catchment (the surface that collects rain).
- 2Gutters and a down pipe carry the water down.
- 3★A filter of pebbles, gravel and sand removes dust and leaves.
- 4The clean water is stored in a sump or tank for use.
- 5★Extra water goes to a recharge pit or well. It soaks into the ground and raises the water table.
★ key step
How to draw a rooftop rainwater harvesting system
- Draw a house with a flat roof and rain lines above it. Label roof (catchment).
- Draw a gutter along the roof edge and a pipe coming down the wall. Label gutter and down pipe.
- At the foot of the pipe, draw a box with three layers. Label it filter: pebbles, gravel, sand.
- From the filter, draw one pipe to a closed tank. Label storage tank (sump).
- Draw another pipe to a pit in the ground filled with stones. Label recharge pit, with arrows down to groundwater.
- Write the title: Rooftop rainwater harvesting.
Traditional water bodies
| Name | What it is | Where |
|---|---|---|
| Eri | A large tank with an earthen bund, storing rain and river water for irrigation; often linked in chains | Across Tamil Nadu, e.g. Chembarambakkam and Madurantakam lakes |
| Oorani | A small village pond, kept mainly for drinking water | Villages across Tamil Nadu, especially dry districts such as Ramanathapuram |
| Kulam (temple tank) | A stone-stepped tank near a temple that stores rain and recharges nearby wells | Mylapore temple tank, Chennai, and most temple towns |
| Kanmoi | A rain-fed tank used for irrigation | Southern Tamil Nadu |
| Kallanai (Grand Anicut) | A stone dam across the Kaveri that diverts water to fields | Thanjavur district |
| Johad, kul, bamboo drip | Earthen check dams; channels from streams; bamboo pipes | Rajasthan; Himachal Pradesh; Meghalaya |
Other ways to save water
- Drip and sprinkler irrigation on farms.
- Desilting and repairing eris and ponds before the monsoon. Villagers did this together in the old practice of kudimaramathu.
- Building check dams across streams.
- At home: fix leaking taps, close the tap while brushing, and reuse washing water for plants.
- Do not dump waste or sewage into rivers and lakes.
After the 2015 Chennai floods and the 2019 water shortage, many families revived rooftop harvesting and recharge wells. The same rain that floods our streets can fill our wells.
2 marks: “What is rainwater harvesting? Write two advantages.” Collecting and storing rainwater for use or to recharge groundwater. It raises the water table and gives water in summer; it also reduces street flooding.
2 marks: “What are eris? How are they useful?” Traditional Tamil Nadu tanks with earthen bunds that store rain and river water. They irrigate fields, recharge groundwater and control floods.
4 marks: “Explain rooftop rainwater harvesting with a labelled diagram.” Roof as catchment, gutters and down pipe, filter of pebbles, gravel and sand, storage tank or recharge pit; raises the water table; labelled diagram.
Catch, carry, clean, keep or recharge: roof, pipe, filter, tank or pit.