What is the term for the pressure that exists in a water supply system when no water is flowing?

The correct term for the pressure that exists in a water supply system when no water is flowing is static pressure. Static pressure represents the potential pressure available in the system and is measured at a standstill, meaning no demand for water is being made. This is important in firefighting because understanding static pressure helps firefighters determine how much pressure is available for use when they connect hoses or equipment to a hydrant.

The other terms have specific meanings that differ from static pressure. Dynamic pressure refers to the pressure in a system when water is in motion, typically used when water is being delivered to a fire scene. Residual pressure refers to the remaining pressure in the system while water is flowing and is crucial for understanding how much pressure is still available to deliver after accounting for losses. Operating pressure is a broader term that can refer to the pressure in the system under normal conditions, typically when water is flowing, instead of the no-flow condition representative of static pressure.