Recharge Pit & Refill the Water Table
Recharges runoff
Enter catchment area, design rainfall, runoff coefficient and pit depth to get the pit volume, the runoff per storm, the pit area and side — so runoff soaks in instead of escaping.
Enter your catchment
Next: dig a ~8.5 m³ pit (1.68 m square × depth), fill with boulder/gravel/sand, and lead roof water in through a desilting/filter chamber.
Size and filter media depend on soil percolation; keep the pit away from foundations and septic systems, and de-silt before each monsoon.
Recharge pit — key facts
- Runoff
- catchment × rainfall × coefficient
- Roof coefficient
- ≈ 0.85
- Size for
- the heaviest storm
- Pit area
- volume ÷ depth
- Fill
- boulder / gravel / sand
- Inlet
- desilting / filter chamber
- Keep away from
- foundations & septic
- Privacy
- Runs in your browser; nothing uploaded
Catch the runoff and put it back in the ground
Every storm that runs off a roof or yard is water lost — unless you give it somewhere to soak in. A recharge pit does exactly that: it collects rooftop or yard runoff, filters it through layers of boulder, gravel and sand, and lets it percolate down to refill the water table instead of escaping. Size it for the heaviest storm so it doesn't overflow, lead the water in through a desilting chamber, and keep it well clear of foundations and septic tanks.
This tool gives the pit volume, the runoff per storm, the pit area, the pit side length and the annual recharge from your catchment area, design rainfall, runoff coefficient and depth. Use it to design a soak pit that recharges a borewell or open well and revives your groundwater. Pair it with the Rainwater Harvesting, Farm Pond and Borewell Yield tools to plan the whole water-storage picture.
Stop losing runoff
Soak storm water in instead of letting it escape.
Size for the storm
Hold the heaviest downpour without overflow.
Refill the water table
Recharge a borewell or open well below.
Dig the right pit
Volume, area and side length to build.
Frequently Asked Questions
What is a recharge pit?+
A recharge pit is a dug structure that captures rooftop or yard runoff and lets it soak into the ground to refill the water table, instead of letting that water run off and escape. Filled with boulder, gravel and sand and fed through a filter chamber, it turns each storm's runoff into stored groundwater you can draw on later.
How is the pit sized?+
Runoff (m³) = catchment area × rainfall × runoff coefficient. You size the pit to hold the runoff from the heaviest design storm, and pit area = volume ÷ depth. The tool chains these so you enter the catchment, the design rainfall, the runoff coefficient and the depth, and it returns the pit volume, area and side length to dig.
What is the runoff coefficient?+
It's the fraction of rain falling on a surface that actually runs off rather than soaking in or evaporating. A hard roof sheds almost everything — about 0.85 — while paved yards are a bit lower and bare soil lower still. Multiplying rainfall by this coefficient gives the runoff the pit must capture from the catchment.
What design rainfall should I use?+
Size the pit for the heaviest storm you expect to capture, not the average shower — that's the peak the pit has to hold so water doesn't overflow and be lost. Use a high one-event rainfall figure typical of an intense local downpour; the bigger the design storm, the larger the pit volume the tool returns.
How deep should a recharge pit be?+
Depth is a trade-off: a deeper pit needs less surface area for the same volume and reaches further toward permeable layers, but is harder to dig and de-silt. Set the depth you can practically build and maintain, and the tool gives the matching pit area and side length to hold the design runoff.
What should the pit be filled with?+
Fill a recharge pit in layers — coarse boulders at the bottom, gravel in the middle and sand near the top — so water filters as it percolates and silt is trapped before it clogs the soil. Lead the runoff in through a desilting or filter chamber, and clean that chamber and the top layer before each monsoon.
Where should I locate the pit?+
Keep the pit well away from building foundations so soaking water doesn't undermine them, and away from septic tanks, soak-aways and any contamination source that could pollute the groundwater. Place it where rooftop or yard runoff can be channelled to it easily, on ground that drains rather than waterlogs.
How much water can it recharge in a year?+
Annual recharge depends on how many storms the pit captures over the season — far more than a single storm's volume. The tool estimates the yearly recharge from your inputs so you can see the cumulative groundwater benefit, not just the one-event capacity, when deciding whether the pit is worth building.
Does this work for a roof, yard or field catchment?+
Yes — enter the catchment area and the runoff coefficient that matches the surface (high for roofs, lower for yards or fields), and the tool sizes the pit for that catchment. A bigger or harder catchment produces more runoff and needs a larger pit; the calculation adapts to whatever you feed it.
Are the figures exact?+
They're solid planning figures. Real recharge depends on soil permeability, the water table depth, how often the pit is de-silted and the actual storm pattern, so add margin and maintain the pit. De-silt before each monsoon, and treat the outputs as a design starting point to confirm against local hydrogeology.