Well Water Flow Rate & Yield Calculator
Calculate well flow rate, specific capacity, and sustainable yield using pumping test data. Enter the pumping rate, static water level, pumping water level, and well diameter to evaluate well performance.
Formulas Used
Drawdown (s):
s = PWL − SWL
Where PWL = Pumping Water Level, SWL = Static Water Level (both measured from surface)
Specific Capacity (Sc):
Sc = Q / s
Where Q = pumping rate, s = drawdown. Units: GPM/ft or L/min/m
Casing Storage Volume:
V = π × r² × (Depth − SWL)
Where r = casing radius. Represents the standing water column volume.
Daily Yield (conservative):
Y = Q × 60 min/hr × 8 hr/day
Based on 8-hour sustainable pumping per day — a standard conservative estimate.
Available Drawdown:
AD = Well Depth − PWL
Remaining buffer before pump intake is exposed.
Assumptions & References
- Pumping test is assumed to have reached approximate steady-state (stabilized water level).
- Specific capacity is calculated at the tested pumping rate; it may decrease at higher rates due to well losses.
- Daily yield uses an 8-hour pumping day as a conservative sustainable estimate per USGS guidelines.
- Casing storage volume assumes a uniform cylindrical casing from static water level to well bottom.
- Performance ratings based on Driscoll (1986) Groundwater and Wells, 2nd Ed., Johnson Screens.
- Specific capacity thresholds (L/min/m): Excellent ≥ 20, Good ≥ 10, Moderate ≥ 4, Low ≥ 1, Very Low < 1.
- Does not account for aquifer type (confined vs. unconfined), well efficiency losses, or seasonal variation.
- For regulatory compliance or water rights, consult a licensed hydrogeologist or well driller.