| Primary value | 20 m³ per 100 m² ((roof area, typical metro)) |
| Applies to | Plots > 100 m² in most metros (varies by city) |
| Exceptions | Mandatory threshold (most cities) → Plot > 100-300 m² |
| Use → Direct recharge to ground OR storage tank | |
| Bengaluru / Chennai (strict) → Compulsory for all new construction | |
| Sizing basis → Some bye-laws specify capacity based on litres/capita/day (e.g., 20-50 lpcd) or a minimum number of rainy days of storage, rather than roof area. | |
| Recharge prohibition → In areas with high water tables or contaminated groundwater, direct recharge to aquifers may be prohibited. Only storage for reuse is permitted. | |
| CGWA NOC → For large projects (industrial, infrastructure, large residential), a No Objection Certificate (NOC) from the Central Ground Water Authority (CGWA) is required, which has its own specific RWH conditions. | |
| Measured as | Storage tank capacity sized as % of expected annual rainfall × roof area × runoff coefficient (~0.85 for terrace). |
| Source | NBC 2016 — NBC 2016 Part 11, Clause 4.10 & Annex C; and specific Municipal/State Bye-laws ✓ Verified |
With many Indian cities facing acute water stress and depleting groundwater tables, rainwater harvesting is a critical sustainability measure. It reduces dependence on strained municipal water supplies and helps replenish local aquifers. Consequently, obtaining an Occupancy Certificate (OC) from most municipal corporations is now contingent on implementing a functional RWH system.
Implementation typically involves storing rooftop runoff in an underground sump for non-potable uses like flushing and landscaping. Any overflow from this storage tank is then directed into percolation pits or recharge wells to augment the groundwater table, a combination often mandated by local bye-laws.