What does residual pressure represent in a water flowing system?

Residual pressure represents the portion of pressure in a water flowing system that remains available for usage after accounting for losses due to friction in the pipes and fittings, as well as losses due to elevation changes (gravity). This is critical for understanding how much pressure is actually usable for delivering water effectively to the intended destination, such as a fire hydrant or sprinkler system.

In practical terms, when water flows through a system, some pressure is consumed by friction within the pipes, which impedes the flow. Additionally, if water has to be lifted or pushed against gravity, that also consumes some of the available pressure. Therefore, residual pressure indicates the remaining pressure that can still be exerted for actual flow or use after these losses have been deducted. This measurement is vital for designing and evaluating water distribution systems to ensure that they meet the required service levels.