Calculators
Water Supply Calculator
Calculate available flow at any desired residual pressure from fire flow test data. Enter your flow test results and the calculator plots the supply curve with elevation correction.
Water Supply Curve Calculator
Q_available = Q_measured x [(P_static - P_desired) / (P_static - P_residual)]^0.54
How it works
The calculator uses the N^1.85 relationship:
Q_available = Q_measured x [(P_static - P_desired) / (P_static - P_residual)]^0.54
- The 0.54 exponent is derived from 1/1.85 (the inverse of the Hazen-Williams exponent)
- Elevation adjustment subtracts 0.433 psi per foot of elevation above the flow test point
- The supply curve table shows available flow at multiple residual pressures for plotting
When to use
- Initial water supply analysis when receiving flow test data
- Comparing supply adequacy across multiple flow test locations
- Determining whether a fire pump is needed before starting full design
- Plotting supply curves for the hydraulic calculation summary
Flow test data age
Most AHJs require flow test data less than 12 months old. Municipal supply conditions change with seasonal demand, new development, and system maintenance. See Water Supply Sources for complete supply analysis methodology.
Related references
- Water Supply Sources — flow test procedures, device losses, safety margins
- Hydraulic Calculations — demand calculations and supply comparison
- Fire Pumps — when supply is insufficient