How do you calculate the potential amount of water to be harvested?

Use the formula: Potential Harvest = Catchment Area × Rainfall × Runoff Coefficient. The Runoff Coefficient is found in Table 1 based on the roof material.

What is a 'first flush' and why is it important?

It's the first spell of rain that washes off debris and pollutants from the roof. The code recommends diverting it (approx. 2.5 mm of rain) to ensure cleaner water is collected for storage (Clause 5.4.1).

Is filtration necessary for harvested rainwater?

Yes, a filter is a critical component to remove suspended pollutants like leaves and dust before the water enters the storage tank or recharge structure (Clause 5.5).

Can harvested rainwater be used for drinking?

Only after proper treatment, including disinfection, to meet the standards of IS 10500. This code primarily covers collection and storage for non-potable uses like flushing, gardening, and washing.

IS 16016

: 2012

Code of Practice for Installation of Rainwater Harvesting Systems in Buildings

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This code provides guidelines for the planning, design, construction, installation, and maintenance of rainwater harvesting systems in buildings. It details system components such as catchment areas, conveyance systems, filters, and storage tanks to promote water conservation and sustainable water management.

Provides guidelines for the installation of rainwater harvesting systems specifically within building premises.

Quick Reference Values

Runoff coefficient for concrete roof0.70 - 0.90

Runoff coefficient for corrugated metal sheets0.70 - 0.90

Runoff coefficient for tiled roof0.75 - 0.90

First flush recommendationDivert first 10-20 minutes of rainfall or 2.5 mm

Recommended pH for harvested rainwater (for non-potable use)6.5 to 8.5

Typical per capita water requirement for storage design135 litres/day

Recommended screen mesh size for inlets1 mm

Key Formulas

Harvestable Water (m³) = Catchment Area (m²) x Annual Mean Rainfall (m) x Runoff Coefficient

Practical Notes

Always incorporate a 'first flush' diverter to prevent the initial, more contaminated rainwater from entering the storage tank. This significantly improves stored water quality.

Regularly clean gutters, downpipes, and filter media, especially before the start of the monsoon season, to prevent clogging and maintain system efficiency.

Verify local municipal regulations, as many now have mandatory requirements for rainwater harvesting in new constructions which may include specific design criteria or subsidies.