Water Conservation, Rainwater Harvesting and Groundwater Recharge
This domain tests conservation, rainwater harvesting and groundwater recharge, including Maharashtra's watershed and Jalyukt Shivar-style interventions. Questions ask where to store water, how to recharge safely and how to avoid maladaptation.
Core rules
- Prefer recharge where the aquifer is transmissive and water is needed; avoid recharging in clay or near contamination sources.
- A rainwater system needs catchment, first flush, filter, storage or recharge pit, and overflow. Rooftop yield = roof area × rainfall × runoff coefficient.
- Recharge structures need desilting and maintenance. Borewell recharge must use filtered water to prevent clogging and contamination.
Worked example
A 100 m2 roof receives 800 mm rain. With a runoff coefficient of 0.8, yield = 100 × 0.8 × 0.8 m = 64 m3/year, or 64,000 L. A recharge pit of 3 m × 3 m × 3 m with 30% void space holds 8.1 m3. One pit cannot absorb the whole roof yield; the design needs a larger pit, multiple pits or storage with controlled overflow. The reasoning separates annual yield from event storage.
Traps
- Installing recharge pits in impermeable clay.
- Omitting first flush and overflow.
- Sending dirty roof water directly into a borewell.
- Assuming every check dam raises groundwater everywhere.