GPM (Gallons Per Minute)
A measure of flow rate, the volume of water a fixture or system delivers each minute, distinct from pressure, which is the force behind it.
Gallons per minute tells you how much water actually moves, while PSI tells you how hard it pushes. A modern showerhead delivers about 1.8 to 2.5 GPM, a kitchen faucet around 1.5 to 2.2, and a bathtub tap 4 or more. These numbers matter most when several fixtures run at once: if the supply line or water heater cannot keep up with the combined demand, you feel it as a shower that goes cold or weak when someone starts the dishwasher.
GPM is the headline spec for sizing equipment. A tankless water heater is rated by how many gallons per minute it can heat across a given temperature rise, so a unit that handles 5 GPM in a warm climate may only manage 3.5 GPM in a cold one where incoming water is icy. Well pumps are rated the same way, and matching pump GPM to a household peak demand is what keeps two showers and a washing machine from draining the system.
Low GPM at a single fixture with normal pressure usually means a restriction: a clogged aerator, a flow restrictor, or scale narrowing the pipe. Low GPM across the whole house points to undersized supply lines, a partly closed valve, or a pump and tank that cannot deliver. Because pressure and flow get confused so easily, naming the right one saves money, the fixes for each are completely different.
Talking to a contractor about this?
Run the project past a licensed plumbing pro first. Calls are answered around the clock and routed to a pro serving your area.
- Pressure Reducing Valve (PRV) : A spring-loaded valve installed on the main line that lowers high municipal pressure to a safe household level, usually preset around 50 PSI.
- Water Hammer : The banging or knocking in pipes that happens when fast-moving water is suddenly stopped by a closing valve, sending a shock wave back through the line.
- Main Shutoff Valve : The valve that stops all water entering the house, typically located where the supply line comes through the wall near the meter or in the basement.
- Angle Stop / Fixture Shutoff : The small individual shutoff valve under a sink or behind a toilet that stops water to that one fixture without shutting down the whole house.