Percolation Tank & Bank Water Underground
Recharges the aquifer
Enter the tank capacity, the fillings per year and the recharge efficiency to get the annual inflow and the annual groundwater recharge that lifts your downstream wells.
Size a percolation tank
Next: plan for ~60,000 m³/year reaching the aquifer; site the tank on permeable strata upstream of the wells you want to revive and desilt the bed each summer.
Efficiency depends heavily on bed permeability and silt load; lined or silted-up tanks recharge far less than the design figure.
Percolation tanks — key facts
- Job
- Hold run-off so it seeps to the aquifer
- Annual recharge
- Capacity × fillings × efficiency
- Fillings
- Times the tank refills in a year
- Efficiency
- ≈ 50–75% percolates
- Best site
- Permeable bed, above target wells
- Benefit
- Lifts the water table in wells below
- Upkeep
- Desilt to keep the bed permeable
- Privacy
- Runs in your browser; nothing uploaded
A tank that is meant to leak
Most water structures try to keep water in. A percolation tank does the opposite: it catches monsoon run-off, holds it for a while, and lets it soak away through a permeable bed into the aquifer below. Through a wet season the tank can fill, drain and refill several times, so the volume it banks underground is its capacity multiplied by the number of fillings — minus what evaporates or spills, which is captured by the recharge efficiency. The water then moves through the ground to the wells downstream, lifting the water table where it matters.
This tool computes the annual inflow, the annual recharge volume, the effective recharge efficiency and the tank capacity from your inputs. Use it to size a tank for the recharge you need and to compare sites. Pair it with the Check Dam, Contour Trench and Recharge Pit tools to build a full watershed recharge plan.
Bank the monsoon
Catch run-off and send it underground.
Multiply with fillings
Several fills a year beat one big tank.
Lift your wells
Recharge raises the water table downstream.
Size with confidence
Annual recharge volume before you build.
Frequently Asked Questions
What is a percolation tank?+
A percolation tank is a small earthen reservoir built across a stream or in a natural depression to catch run-off. Unlike a storage tank meant to hold water for use, its job is to detain the water just long enough for it to seep down through the bed and recharge the aquifer below, so the benefit shows up in wells rather than at the surface.
How is annual recharge calculated?+
Annual recharge = tank capacity × number of fillings per year × recharge efficiency. The capacity is what the tank holds when full, the fillings count how many times run-off refills it through the rains, and the efficiency is the fraction that actually percolates rather than evaporating or spilling. The tool multiplies these to give the volume recharged each year.
What does fillings per year mean?+
A percolation tank often fills, percolates and empties more than once in a wet season — each fresh spell of rain can refill it. The number of fillings is how many full tank-volumes pass through in a year. A tank that fills three times effectively processes three times its standing capacity, which is why fillings matter as much as size.
What is recharge efficiency?+
Recharge efficiency is the share of the inflow that genuinely soaks into the ground. The rest is lost to evaporation from the open water and to any overflow. It depends on the permeability of the tank bed, the depth of water, the climate and how silted the tank is; typical planning values run from about 50% up to 75% for a well-sited, desilted tank.
How does a percolation tank lift downstream wells?+
The water that percolates moves down to the water table and then slowly sideways and downhill through the aquifer. Wells dug into that aquifer downstream see the water table rise, recover faster after pumping and stay productive later into the dry season. One well-placed tank can improve a whole cluster of wells below it.
Where should a percolation tank be sited?+
Site it on permeable ground — weathered or fractured rock, sandy or gravelly beds — where water can actually soak in, and upstream of the wells you want to benefit. A clayey, tight bed makes a poor percolation tank because the water just sits and evaporates. A quick infiltration test of the proposed bed is worth doing.
How is it different from a farm pond or storage tank?+
A farm pond or storage tank is lined or sited to hold water so you can pump it out later for irrigation. A percolation tank is deliberately built where the bed leaks, so the water disappears underground on purpose. The two have opposite design goals — one keeps water in, the other lets it out into the aquifer.
Does the tank need maintenance?+
Yes — silt carried in by run-off settles on the bed and seals it, cutting the percolation rate over time. Periodic desilting restores the infiltration capacity and, as a bonus, the removed silt is good fertile soil for fields. Keeping the spillway and bund in repair also protects the structure from breaching in heavy flows.
Are the figures here exact?+
They are planning estimates built from your capacity, fillings and efficiency. Real recharge varies with rainfall in a given year, the changing bed permeability as silt builds up, and the aquifer’s ability to accept water. Use the result to compare designs and size structures, and refine the efficiency from local monitoring where you have it.