Low Water Pressure: How to Find Out Why and Fix It
Low pressure at one faucet, on one floor or in the whole house each point to different causes. Narrow it down, then clean, adjust or replace the right part.
- Difficulty
- Easy
- Time
- 10 minutes for an aerator; 1–2 hours to test the whole system
- Typical cost
- $0–$15 for aerators and cleaning; $15–$30 for a hose-bib pressure gauge
Weak water pressure turns a shower into a chore and makes a dishwasher or washing machine take longer to fill. The causes range from a ten-minute cleaning job to a problem with the city supply, and the fastest way to the right one is to notice exactly where the pressure is low.
Start with where the problem is
| Where pressure is low | Most likely causes |
|---|---|
| One faucet or one showerhead | Clogged aerator or showerhead, partially closed fixture valve, worn cartridge |
| Hot water only, everywhere | Water heater inlet valve partly closed, sediment in the heater, hot-side supply issue |
| One bathroom or one floor | Partially closed branch valve, failing old galvanized pipe, a leak on that branch |
| The whole house, suddenly | Utility work or a main break, main shutoff not fully reopened, failing pressure regulator |
| The whole house, gradually | Pressure regulator wearing out, mineral buildup in old pipes, hidden leak |
Ask a neighbor whether their pressure is also low. If it is, the problem is probably on the utility side and a call to your water provider will tell you if there is a known issue.
Fix 1: Clean the aerator or showerhead
The aerator is the small screen at the tip of the faucet spout. It collects grit and mineral scale, especially after plumbing work or a water main repair.
- Unscrew the aerator by hand, or with pliers wrapped in tape to protect the finish.
- Rinse out loose debris. Soak the screen in white vinegar for an hour to dissolve scale, then scrub with a toothbrush.
- Reinstall and test. If it is damaged, replace it with one of the same thread size.
For a showerhead, unscrew it from the arm, or tie a plastic bag of vinegar around it overnight. Brush out the nozzles before reattaching. Keep in mind that newer showerheads and faucet aerators are designed to use less water; the EPA’s WaterSense program labels models that deliver good performance at lower flow, so a modern fixture with lower flow is not automatically a pressure problem.
Fix 2: Check the valves
Every fixture has a supply valve, and the house has a main valve. After a repair, someone may have left a valve partly closed.
- Make sure the valves under the sink or behind the toilet are fully open (counterclockwise until they stop).
- Confirm the main shutoff is fully open. A gate valve should be turned counterclockwise all the way; a ball valve’s lever should line up with the pipe.
- If only the hot side is weak everywhere, check the valve on the cold inlet of the water heater.
Fix 3: Measure the house pressure
A hose-bib pressure gauge threads onto an outdoor faucet or the washing machine valve. With no other water running, open the valve and read the gauge. Your water utility can tell you the normal supply pressure for your area, and your fixtures’ manuals list the pressure range they are designed for. A reading well below the utility’s figure points to a supply or regulator problem; a reading that drops sharply when another fixture runs suggests restricted pipes.
If your home has a pressure-reducing valve (a bell-shaped fitting on the main line after the shutoff), it may have an adjustment screw on top. Turning it changes the house pressure, but regulators can fail internally, and adjusting a failing one rarely fixes it for long.
Fix 4: Rule out a leak
A leak on the supply side steals pressure and money. The EPA recommends reading your water meter before and after a two-hour period when no water is being used. If the reading changes, look for running toilets, wet spots in the yard along the service line, damp areas in the basement or crawlspace, and dripping supply connections.
Fix 5: Consider the pipes themselves
Older homes with galvanized steel pipe can lose pressure gradually as the inside of the pipe corrodes and narrows. The sign is pressure that has slowly declined for years, often worse on upper floors, and sometimes rusty water when a faucet first opens. Cleaning will not fix this; sections of pipe need to be replaced.
Common mistakes
- Replacing a faucet when the aerator was clogged. Always check the aerator first.
- Removing flow restrictors from showerheads. It can waste water and may conflict with local plumbing rules.
- Cranking up a pressure regulator. Too much pressure stresses fixtures, supply lines and appliance valves.
- Ignoring a sudden house-wide drop. It can mean a main break or a serious leak.
When to call a plumber
Call a plumber if the measured house pressure is very low or very high, if the pressure regulator needs replacing, if you suspect a leak you cannot find, or if old galvanized pipe is the cause. Problems on the street side of the meter belong to your water utility, so call them first if neighbors have the same issue.