Low Water Pressure? How to Find the Cause and Fix It
Weak water pressure has a handful of common causes — from a clogged aerator to a failing pressure regulator. Here's how to diagnose whether it's one fixture or the whole house.
Weak water pressure is one of the most common — and most diagnosable — plumbing complaints. The single question that determines everything is: is it one fixture, or the whole house? Answer that first and you'll know whether you're looking at a two-minute cleaning or a valve replacement.
Step 1: one fixture or whole house?
Run several faucets around the home, hot and cold.
- Just one fixture weak → a local problem (clogged aerator, showerhead, or supply valve). Skip to "Fixing one weak fixture."
- Weak everywhere → a whole-house problem on the main line (shutoff valve, pressure regulator, supply, or a leak). Skip to "Fixing whole-house low pressure."
Fixing one weak fixture
Nine times out of ten, it's mineral buildup.
Clean the aerator. The aerator is the little screen that threads onto the faucet tip. It clogs with scale and grit:
- Unscrew it by hand (or with tape-wrapped pliers to avoid scratches).
- Soak it in white vinegar to dissolve the hard water scale, then brush and rinse it.
- Thread it back on and test.
Clean the showerhead the same way — unscrew it, or tie a vinegar-filled bag around it overnight to dissolve the deposits clogging the nozzles.
Check the fixture's shutoff valves. Under the sink (or behind the toilet), make sure the small supply valves are turned all the way open, and that the supply lines aren't kinked.
If one fixture stays weak after all that — especially in an older home — corroded galvanized pipe may be narrowing the line, which is a plumber's job.
Fixing whole-house low pressure
When everything's weak, work down the main line.
1. Open the main shutoff fully. A main water shutoff that's only partly open throttles the whole house. Make sure it's turned all the way on. (If you're not sure where it is, see how to shut off the water to your house — and the locate & test your main water shutoff task.)
2. Test the pressure. Buy an inexpensive water-pressure gauge, screw it onto an outdoor spigot, and open the tap. Normal is 40–60 psi. This is the check your home's water pressure task, worth doing once a year.
3. Check the pressure regulator. If pressure reads low (or wildly high) and your valves are open, suspect the pressure regulator — the bell-shaped valve where the main line enters, near the shutoff. These fail over time and are a common, fixable cause of sudden whole-house pressure changes; they can be adjusted or replaced.
4. Rule out a leak. A hidden leak steals pressure. Check your water meter with everything off — if it's still moving, water is escaping somewhere. Look for damp spots, and inspect supply lines.
If you're on a well
A private well has its own pressure system. Whole-house low pressure there usually means a waterlogged pressure tank or a misadjusted pump pressure switch — see the check the well pressure tank task and well water testing for the broader system.
Don't ignore pressure that's too high
While you've got the gauge out: pressure above 80 psi is its own problem. It stresses every pipe, joint, appliance, and supply line in the house and is a leading cause of burst supply lines. If your gauge reads high, that same pressure regulator should be bringing it down — and a failed one is why it isn't. For the full routine, see the plumbing system overview.
Make it automatic
Build your free Owner Tools plan and we'll remind you to test your water pressure, clean aerators, and inspect supply lines on schedule — so weak (or dangerously high) pressure gets caught early. No login, no address required.