Low Water Pressure in the House: Six Causes, Ranked

One fixture only: it's the aerator

If pressure is fine everywhere else, unscrew the aerator from the affected faucet and look at it. Mineral scale and small debris collect there and choke the flow. Soak it in vinegar or replace it. Showerheads clog the same way.

Whole house, came on gradually: corroded pipes

This is the classic galvanized steel story. Galvanized pipe corrodes from the inside, and over decades the internal diameter closes up with rust and scale. Pressure drops slowly enough that nobody notices until a guest mentions it. Brown or rust-tinted water at first draw is the confirming symptom, and the fix is repiping rather than patching.

Whole house, came on suddenly: the regulator or the main

A pressure reducing valve that fails will drop pressure across the whole house at once. So will a partially closed main shutoff — worth checking first, because it's free. A sudden drop can also mean a break in the service line between the meter and the house.

Hot water only: it's the water heater

If cold pressure is normal but hot is weak, sediment in the tank or a failing dip tube is restricting flow. Flushing the tank often restores it.

Pressure drops only when other fixtures run

Undersized supply lines or partially closed valves cause this. It's common in homes where a bathroom was added without upsizing the trunk line.

Everything checks out but pressure is still low

At that point it's worth checking the meter with everything shut off. If the meter is still turning, water is going somewhere it shouldn't, and a leak on the service line will pull pressure down across the house.