A water flow test is a way to measure the water supply available at a building site, usually for the purposes of installing a water based fire protection system (fire sprinkler system).
The most common test involves measuring the flow of water flowing out of a municipal fire hydrant (measured in gallons per minute) while recording how much the water pressure has dropped (from no water flow to test flow). When the results are collected carefully, formulas can be applied to figure the varying pressure(s) that will be available when different amounts of water flow are used from the same source. A process to perform a water flow test is explained in the model fire codes as published by NFPA (National Fire Protection Association).
If a water supply source is considered weak compared to what is required by the sprinkler system design hydraulic calculation, the water pressure can be boosted by means of a fire pump.