A portion of total available water pressure that is not used to overcome friction loss is known as:

Answer: C — Residual Pressure

The portion of total available water pressure that is not used to overcome friction loss is referred to as residual pressure. Residual pressure represents the pressure remaining in the system after some of it has been used to overcome friction within the hoses, fittings, and other components during water flow. It is critical for determining the amount of water that can be effectively delivered at the nozzle during firefighting operations. Understanding residual pressure is essential for maintaining the efficiency of water delivery systems. It indicates the effectiveness of the water supply and enables firefighters to assess whether adequate pressure remains for effective operation at the nozzle. To maintain effective firefighting capabilities, operators must be aware of how much residual pressure is available after accounting for any pressure lost due to friction, ensuring that sufficient pressurized water can still reach the fire.