Rainwater Harvesting
Rainwater harvesting captures rooftop and surface runoff and either stores it for reuse or recharges it into the aquifer — a bye-law mandate for most sizeable plots and a compliance companion to any CGWA groundwater NOC.
Why it matters on an MEPF project
The arithmetic is generous: roof area (m²) × rainfall (mm) = litres/year before losses, which for industrial roofs means thousands of kilolitres. Engineered properly — first-flush diversion, staged filtration, storage sized to a useful buffer with overflow to recharge — it is the rare compliance item with a direct payback wherever tanker or borewell water carries real cost.
The compliance web is threefold: ULB bye-laws check it at plan sanction and completion; CGWA NOCs for groundwater abstraction carry recharge obligations; and green ratings credit it. The failure mode is the token pit — built to pass a drawing, silted in two monsoons — which satisfies nobody at renewal and wastes the one obligation that could pay rent.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Yield | Roof m² × rainfall mm × collection efficiency | hydrology arithmetic |
| Storage vs recharge | Storage where reuse value exists; recharge for surplus/mandate wording | design decision |
| Water quality | First-flush diversion + filtration staged to end-use | design practice |
| Compliance | Bye-law verification; CGWA recharge linkage | ULB bye-laws / CGWA directions |
Common mistakes
- The decorative pit with no first-flush, no filter, no desilting access.
- Storm drains sized to averages, flooding in the first cloudburst.
- Recharge structures placed near contamination sources.
- No meter on the reuse line — savings remain a belief, not a number.
Related on this site
Frequently asked
Is rainwater harvesting mandatory for factories?
Above plot-size thresholds in most states/ULBs, yes — checked at plan sanction — and effectively yes wherever a CGWA NOC governs your borewells. The thresholds are local; read your bye-law text.
Storage or recharge — which should I build?
Usually both: storage to the volume you can usefully reuse (flushing, cooling make-up, wash-down), overflowing to engineered recharge. Our rainwater calculator sizes the split from your roof and rainfall.
Standards referenced: ULB building bye-laws · CGWA directions