How to use this calculator
- Do a field test: pour clean water into the bore and note the volume and time, or fill it and time the fall in level.
- Enter the catchment area and a design rainfall intensity.
- Read the recharge rate and the number of wells needed.
How do you calculate the recharge rate of a borewell?
Rate (L/min) = volume poured ÷ time
Falling level: volume = π × D² ÷ 4 × fall in level
Peak runoff (m³/h) = A × i × C ÷ 1,000
Wells = peak runoff ÷ rate per well (rounded up)
Worked example
With test method: Pour test: water poured at a steady level, water poured 2,000 litres, time taken 10 minutes, catchment draining to the wells 2,000 m², design rainfall intensity 50 mm/h, runoff coefficient 0.8:
Recharge rate per well: 12 m³/h
The calculator also gives recharge rate 200 L/min; per day of continuous inflow 288 m³/day; peak storm runoff 80 m³/h.
Assumptions and limits
- The rate drops over time as fine silt clogs the aquifer face; plan for 50 to 70% of the test rate after a few seasons unless filters are maintained.
- A short test overstates rates in fractured rock; repeat over an hour where possible.
Frequently asked questions
How much water can a recharge borewell take?
In alluvial or fractured aquifers a 150 mm recharge bore often accepts 5 to 30 m³/h. Hard rock with few fractures may take under 2 m³/h. Only a field test tells you.
Can I recharge rainwater into a working borewell?
Yes, roof water can be recharged into a working bore through a filter, but keep it separate from any drinking water intake, and never send road runoff or first flush water into it.
What filter is needed for borewell recharge?
A desilting chamber followed by a graded filter of boulders, gravel and coarse sand, or a commercial cartridge filter for roof water, is standard in CGWB guidance.
References
- CGWB, Manual on Artificial Recharge of Ground Water (2007)
- CGWB, Master Plan for Artificial Recharge to Groundwater in India (2020)