A pressure-reducing valve (PRV) is a bell-shaped, spring-loaded valve on the main water line, just after the meter, that lowers incoming municipal pressure to a safe household level, commonly set between 50 and 60 psi. Model plumbing codes such as the IPC and UPC generally require one when static street pressure exceeds 80 psi.
Why it matters to you
Pressure above 80 psi strains supply lines, faucet cartridges, toilet fill valves, and the water heater's T&P valve, so a failing PRV can show up as drips and leaks at several fixtures at once.
Practical guidance
Screw a pressure gauge onto an outdoor hose bib to read your static pressure; a reading above 80 psi, or one that creeps up overnight, means the PRV needs adjustment or replacement. A closed system with a PRV may also need a thermal expansion tank at the water heater.