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.
The main shutoff valve is the single most important valve in your home, because it is what you reach for the moment a pipe bursts or a fixture floods. It sits on the main supply line, usually just inside the foundation wall, in a basement, crawl space, or utility area, and often near the water heater. There is frequently a second shutoff on the street side at the meter, but the interior valve is the one a homeowner uses in an emergency.
Two valve types are common. Older homes have a gate valve, identified by a round wheel handle that turns several times to close. Gate valves are notorious for seizing or failing to seal after years of disuse, so the one time you need it in a flood may be the one time it will not turn. Newer installs use a quarter-turn ball valve with a lever handle that moves ninety degrees from open to closed. Ball valves are far more reliable and are the standard upgrade when an old gate valve is replaced.
Every household should know where this valve is and confirm it actually works before an emergency. Exercising it once or twice a year, turning it fully off and on, keeps the mechanism loose and surfaces a failing valve on your schedule rather than during a 2 a.m. burst pipe. If the handle is hard to turn, drips from the stem, or will not fully stop the flow, it is at the end of its life.
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- Water Pressure : The force that pushes water through your pipes and out of fixtures, measured in pounds per square inch (PSI) and ideally sitting between 40 and 60 PSI in a home.
- PSI (Pounds per Square Inch) : The standard unit for measuring water pressure, where residential plumbing typically targets 40 to 60 PSI and code limits incoming pressure to 80 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.
- 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.