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Recharge pit size calculator

Pick your district and enter your roof area. The calculator fills in 20 years of average rainfall, works out how much water your roof sheds, how many recharge pits it needs and what they cost.

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Your roof

Rainwater from this roof a year
–
Add the rainfall
In one heavy storm (25 mm)
3.0 m³
2,961 litres in an hour
Recharge pits needed
1 pit
2 × 2 × 2.5 m, each with a 120 ft recharge bore, and 1 filter chamber
Cost with GST
₹1.1 lakh to ₹1.7 lakh
Pits, media, bores, filters and piping at our current rates

Haryana: rainwater harvesting is mandatory for rooftop area of 100 sq m and above. Read the rules

Get a quote for thisCost in Gurugram

How the numbers work

Water a year = roof area × yearly rainfall × runoff factor. 1 mm of rain on 1 m² is 1 litre, and a concrete roof sheds about 85% of it.

Pits are sized for one heavy storm of 25 mm in an hour. A 2 × 2 × 2.5 m pit filled with boulders and gravel holds about 4 m³ of water, and its recharge bore drains about 2 m³ an hour, so each pit takes about 6 m³ in that hour.

Cost uses our current rates for the pit, filter media, the recharge bore per foot, filter chambers and piping, with 18% GST. A survey confirms the bore depth and the number of pits.

Check the numbers for your area

Frequently asked questions

How do you calculate the size of a recharge pit?

Work out the runoff from one heavy storm (roof area × 25 mm × runoff factor), then divide by what one pit can take in that hour: about 6 m³ for a 2 × 2 × 2.5 m pit with a recharge bore. Round up to whole pits.

How much rainwater can I harvest from 1,000 sq ft of roof?

1,000 sq ft is 93 m². At 700 mm of rain a year and a runoff factor of 0.85, that is about 55,000 litres a year.

How many recharge pits does a 200 sq yd house need?

Usually one. A typical 200 sq yd house has about 130 m² of roof, which sends about 2.8 m³ of water in a heavy storm, under half of what one pit takes.

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