Rainwater From Parking Calculator
A parking area is a big catchment. Enter its size, your city’s annual rainfall and the surface, and this estimates how much rainwater you could harvest in a year for storage or groundwater recharge.
The parking / driveway surface that drains to your collection point.
Enter your city’s figure — e.g. roughly 800–1200 mm in much of the plains, far higher on the coast and hills.
Runoff coefficient 0.85 — a sealed surface sheds more to collect; a permeable one lets more soak in on the spot (which also recharges groundwater).
About 306 kL (cubic metres) — roughly 30.6 water tankers.
Formula: area × rainfall × runoff (0.85) × collection efficiency (0.8). Most of India’s rain falls in a few monsoon months, so real capture also depends on your tank size, first-flush and a recharge pit for the overflow.
Indicative only. This is the standard annual estimate, not a sized system. It does not set your tank volume, recharge-pit design, filtration or first-flush, and car-park runoff must pass a silt trap and an oil interceptor before it is stored or recharged. Rainwater harvesting is often mandatory above a plot size — confirm the requirement and the design against your local bye-laws and with a professional.
Related Guides — Deep-dive reading
Parking Drainage and Stormwater in India: Channels, Oil Separators and Rainwater (2026)
How to get water OFF and OUT of a car park safely, and put it to use — surface falls to the drains, the critical grated channel at the foot of every ramp, trench vs point drains, the oil and petrol interceptor that keeps runoff clean, silt traps, municipal stormwater vs on-site recharge, rainwater harvesting from the parking catchment, and monsoon flood resilience for basements.
ParkingPercolation Tanks & Ponds in India: Recharging Groundwater at Plot, Farm and Watershed Scale
A professional guide to percolation tanks — impounding monsoon runoff in a shallow surface basin so it slowly infiltrates and recharges the aquifer. How they work, where they suit, siting, indicative sizing, silt management and how they relate to check dams.
PlumbingRainwater Harvesting Guide for India: Catchment, Storage, Recharge & Bye-laws
The section pillar for rainwater harvesting — why it matters for water security and groundwater, the full catchment-to-store-or-recharge chain, the two paths of using rain versus recharging aquifers, indicative yield and sizing, first-flush and filtration, maintenance, and the mandatory-RWH reality in Indian cities.
PlumbingRelated Tools — You may also find these useful
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