Water Sources
Hydrant
A hydrant is a pressurized connection to the water main, the most common engine supply. Its real strength shows not in its static reading but in how far the pressure drops once you flow water.
A hydrant delivers water under the main's own pressure, so the pump only has to add the difference to reach the discharge pressure it needs. How much a hydrant can give depends on the size and condition of the mains feeding it.
Read a hydrant by comparing static and residual: a small drop under flow means strong reserves, a large drop means you are near its limit. That comparison estimates how many more lines the hydrant can support.
Where this shows up
Calculator
Hydrant Available WaterScenario
Hydrant Transition