What Causes Low Water Pressure?

Short answerLow pressure at one fixture is usually a clogged aerator, showerhead or cartridge. Low pressure throughout the house usually comes from a failing pressure-reducing valve, a partly closed main shutoff, a leak in the service line, or corroded galvanized pipe.

Start with where it happens

Turn on several faucets. If only one is weak, the problem is at that fixture. If they're all weak — especially upstairs or when two run at once — the problem is in the supply.

One fixture

Unscrew and rinse the faucet aerator
Soak the showerhead in vinegar to dissolve scale
A single-handle faucet with low flow on one side may need a new cartridge

Whole house

Check that the main shutoff is fully open. Many homes have a pressure regulator on the main line; when it fails, pressure can drop — or climb dangerously high. A drop that happened suddenly can also mean a leak in the service line between the meter and the house.

Old pipe

In homes with galvanized steel supply pipe, pressure fades slowly over years as rust narrows the inside of the pipe. Cleaning doesn't fix it; repiping does. Homes on private wells have their own causes, usually the pressure tank or pressure switch.

What a plumber can fix

The plumber measures static pressure at a hose bib with a gauge. Low readings throughout the house point to a failing pressure-reducing valve, a partly closed main valve or a leak in the service line. Low pressure at one fixture usually means a clogged aerator or cartridge. Corroded galvanized pipe in older homes may need repiping.