Low water pressure: find the cause in 10 minutes

One faucet or the whole house?

Portland’s water utility puts it simply: if some faucets have weak flow while others are normal, the problem is in the plumbing at those faucets, not the city supply. The Las Vegas Valley Water District says that when pressure drops at a property, the cause is usually in the home’s own plumbing rather than the utility’s system.

1. Clean the aerator

The aerator is the small screen at the tip of a faucet. Minerals and debris collect in it, especially after work on water mains. The Las Vegas district notes that low pressure at only some faucets may simply be a clogged aerator. Unscrew it (wrap the jaws of pliers in tape to avoid scratches), rinse or soak the screen, and screw it back. Showerheads clog the same way.

2. Check the valves

Portland’s utility advises making sure all water valves inside the home are fully open. A main shut-off or a fixture shut-off left partly closed after a repair is a common cause. Know where your main valve is: WSSC Water compares knowing how to close it to knowing how to reset a circuit breaker. SFPUC says many main valves are outside or just inside the home, in line with the water meter; WSSC notes that in crawl-space or slab homes it is often near the water heater or under the kitchen sink.

3. Only the hot water is low?

Low pressure on hot water only points to the water heater – a partly closed valve on it, or sediment. See no hot water.

What is normal pressure?

It depends on where you live. Portland keeps most homes between 40 and 80 psi; Phoenix considers 40 to 100 psi acceptable. Phoenix also notes some swings are normal – pressure can dip in the early morning when many people are getting ready at once. A plumber can measure your pressure with a gauge that screws onto a hose bib.

The pressure-reducing valve (PRV)

Many homes have a pressure-reducing valve on the main line. The Las Vegas district says it sits on the homeowner’s side of the meter, often near the water heater, a softener or where the line enters from the meter. A failing PRV can cause low pressure, or pressure that is too high. Too high matters too: the district warns that sustained pressure above 80 psi can damage plumbing and fixtures. Portland notes you may need to install or repair a PRV if pressure bothers you; that is a plumber’s job.

Could it be a leak?

A sudden drop with no explanation, a higher water bill, damp spots, or the sound of running water when everything is off can mean a leak in the supply line. Our leak guide shows how to check with your water meter.

When to call

• Call the water utility if neighbors also have low pressure or there is work on the street.
• Call a plumber if the whole house is low and the valves are open, the PRV may be failing, pressure is above 80 psi, older galvanized pipes are corroding inside, or you suspect a leak.