Percolation tanks are artificial reservoirs widely used across India as a traditional yet effective method for groundwater recharge. Unlike conventional irrigation tanks that store water for direct use, percolation tanks are designed to capture monsoon runoff and allow it to gradually seep into the soil, replenishing underground aquifers.

These structures play a critical role in water-scarce regions of India, particularly in states like Maharashtra, Karnataka, Andhra Pradesh, and Madhya Pradesh. By facilitating natural infiltration, they help mitigate drought conditions, support agricultural activities, and contribute to soil conservation and ecological balance. Studies have shown that percolation tanks have significantly enhanced groundwater availability over decades, making them an essential component of India's rainwater harvesting and water management strategies. Small tanks (under 40 hectares) have increasingly been converted into percolation tanks as part of managed aquifer recharge (MAR) initiatives.

Experimental sites (tanks we have monitored)

Key finding

Our studies reveal that infiltration rates in percolation tanks built on crystalline rock are relatively low, with evaporation rates sometimes approaching infiltration levels, as observed in the Tumulur basin (Efficiency = 56%).

In the Choutuppal basin, infiltration rates were initially higher (95% at the start) due to feeding from the Musi River, which brought large water volumes (up to 3m water depth). However, monitoring showed a rapid decline in infiltration efficiency over time: rates dropped from 250 mm/day during initial filling phases to less than 150 mm/day thereafter. The proportionality coefficient linking infiltration rate to water height decreased significantly after 80 days, as suspended materials from the Musi River quickly clogged the tank bottom.

Similarly, Gajwel basins exhibited very low infiltration rates, with evaporation accounting for up to 35% of harvested water.

Given that the state contains over 200,000 such tanks, this raises critical questions about their maintenance and actual role in the regional hydrological balance. The fundamental question remains: are these truly infiltration tanks, or merely evaporation tanks?

(Efficiency is defined as the ratio between infiltration and total amount of water inflow)

Key publications