Water Sources
Available Fire Flow
Available fire flow is an estimate of how much more water a hydrant can still deliver, based on how far its pressure dropped between static and residual. A small drop means a lot left; a large drop means little.
Rather than guess, the operator measures: note the static pressure, flow a known line, read the residual, and the size of that drop estimates how many more lines of similar flow the hydrant can support.
It turns a vague sense of a 'good' or 'bad' hydrant into a number the operator can plan around. Knowing the available flow tells you whether the hydrant can feed another attack line or a master stream before you commit to it.
Where this shows up
Calculator
Hydrant Available Water