Low Water Pressure: Causes, Diagnosis, and Fixes

Low water pressure has one of six common causes: a clogged faucet aerator, a failing pressure-reducing valve (PRV), a partially closed shutoff or meter valve, corroded galvanized pipe, a hidden leak, or a temporary problem with your municipal supply. The fastest way to narrow it down is to ask one question first: is the weak pressure at a single fixture or across the whole house? Related: a failing pressure reducing valve.

First, know your normal: 40 to 60 psi

Before you diagnose anything, get a real number. Normal residential water pressure sits between 40 and 60 psi, and most US plumbing code (both the IPC and UPC) caps static pressure at 80 psi, which is why any home reading over 80 is required to have a pressure-reducing valve. Below 40 psi is where showers go weak and appliances complain.

Buy a water pressure gauge for $10 to $15, screw it onto an outdoor hose bib or the washing-machine cold tap, and open that tap fully with everything else off. That reading is your baseline. Guessing by how the shower feels wastes an afternoon; a two-dollar gauge reading turns a vague complaint into a fixable fault.

The one question that splits every diagnosis: one fixture or the whole house?

Whether the problem is at one fixture or everywhere tells you where to look before you touch a tool. One weak faucet is a local blockage at that fixture. Weak pressure everywhere points to the main supply, the PRV, the meter valve, whole-house corrosion, or the utility. Walk the house and test the kitchen, a bathroom sink, the shower, and an outside spigot, hot and cold at each.

If only one tap is weak, skip straight to the aerator and cartridge section. If several or all are weak, work the whole-house checks. If only the hot side is weak at multiple fixtures, the water heater is the suspect, not the pressure into the house.

The six causes, by scope and fix

Each cause tends to show up either at one fixture or across the whole house, and each has a different fix and cost. Use this table to match your symptom to the likely cause, then jump to the section that fits. Costs are typical US ranges and vary by region and access.

The diagnostic, in order

Run these steps top to bottom and stop at the one that fixes it. The order moves from free and instant to expensive and slow, so you rarely reach the bottom. Do the whole-house walk-through first so you know which branch of the tree you are on.

1. Test every fixture, hot and cold, and note whether the problem is one fixture or the whole house.
2. Single fixture: unscrew the aerator or showerhead, check for grit and scale, soak it in white vinegar 30 minutes, and reinstall.
3. Single fixture still weak: check the small supply stop under the sink is fully open, then suspect the faucet cartridge.
4. Whole house: confirm the main shutoff and the meter valve are open all the way (lever parallel to the pipe, or wheel turned fully counterclockwise).
5. Put a gauge on a hose bib and read the static psi with all other taps off.
6. Under 40 psi everywhere: locate the pressure-reducing valve (usually just past the main shutoff) and test or adjust it.
7. Pressure fine at the meter but weak inside: suspect corroded galvanized pipe or a hidden leak.
8. Check for a leak: shut every tap and water-using appliance, read the meter, wait two hours with no use, and read again. Movement means a leak.
9. Nothing on your side explains it: call the water utility and ask neighbors whether they see the same drop.

Clogged aerator or showerhead (single fixture)

A single weak faucet is almost always a clogged aerator, the little screen where water exits the spout. Hard water leaves mineral scale that narrows the openings until flow trickles. Unscrew the aerator by hand or with taped pliers, rinse out the grit, soak the parts in white vinegar for 30 minutes to dissolve scale, scrub with an old toothbrush, and reinstall. A new aerator costs $2 to $10 if the old one is corroded.

Fouled cartridge or a half-closed stop (single fixture)

If the aerator is clean and one tap is still weak, check the shutoff stop under that sink is open all the way, since a half-closed stop throttles flow. If the stop is open and pressure is still poor, the faucet cartridge is likely fouled or worn, restricting flow inside the valve body.

Failing pressure-reducing valve (whole house)

A pressure-reducing valve steps down high street pressure to a safe household level and is the most common cause of gradual, whole-house pressure loss. Most PRVs are preset near 50 psi, adjustable roughly 25 to 75 psi, and they wear out in about 7 to 12 years. Find the bell-shaped brass valve just after the main shutoff.

Partially closed main or meter valve (whole house)

The simplest whole-house cause is a valve that is not all the way open, common right after plumbing work or a water shutoff. Check the main shutoff inside the house and the meter valve at the street. A ball-valve lever should sit parallel to the pipe; a round wheel valve should be turned fully counterclockwise. The meter-side valve belongs to the utility, so if it is stiff or partly closed, call them rather than forcing it.

Corroded galvanized pipe (whole house or one branch)

Galvanized steel pipe corrodes and scales up on the inside over 40 to 50 years, and the bore can narrow to a pinhole. Homes built before roughly 1960 often still have it, and the pressure decline is slow and permanent, sometimes worse on the upstairs or far-end branches. Cleaning does not fix a rusted-shut pipe.

Hidden leak (whole house)

A hidden leak bleeds off pressure and shows up as a climbing water bill, a running meter, or a damp spot. Confirm it with the meter test: shut every tap and appliance, note the meter, wait two hours using no water, and check again. Any movement means water is escaping somewhere. Our guide to confirm a hidden leak with your meter walks through the tells and how to read the dials.

Municipal supply issue (whole house and your neighbors)

Sometimes it is not your plumbing at all. A water-main break, hydrant flushing, a repair, or high peak-hour demand can drop pressure across a whole street. The tell is that the drop was sudden and your neighbors feel it too. Call your water utility to ask about known issues and the pressure they deliver to your area.

Low hot-water pressure only

If cold runs strong but hot is weak at several fixtures, the water heater side is the problem, not the pressure coming into the house. Sediment in the tank bottom, a partly closed shutoff on the heater, or clogged heat-trap nipples restrict hot flow. Flushing the tank clears sediment and is worth doing yearly as part of a seasonal plumbing maintenance checklist.

When to call a plumber

Call a licensed plumber when the gauge reads under 40 psi and the PRV adjustment does nothing, when the meter test confirms a hidden leak you cannot see, or when corroded galvanized pipe means a repipe. A pro can also test static and flowing pressure, isolate which branch is failing, and size a booster pump if the utility genuinely delivers low pressure.

Frequently asked questions

What is considered low water pressure?

Below 40 psi is low. Normal residential water pressure runs 40 to 60 psi, and most plumbing code caps it at 80 psi, which is why homes over 80 psi need a pressure-reducing valve. Buy a $10 to $15 gauge that screws onto a hose bib or washing-machine tap to read your actual number instead of guessing.

Why is my water pressure suddenly low?

A sudden drop across the whole house usually points to a failing pressure-reducing valve, a partially closed main or meter valve, or a problem on the utility side. A sudden drop at one fixture is almost always a clogged aerator or cartridge. If pressure fell everywhere overnight with no work done, call your water utility first, then test your PRV.

How do I fix low water pressure in my whole house?

Work in order: confirm the main and meter valves are fully open, put a gauge on a hose bib to read psi, then test the pressure-reducing valve. If the gauge reads under 40 psi and the PRV is set correctly, adjust or replace the PRV, a $250 to $400 job. If pressure is fine at the meter but weak inside, suspect corroded galvanized pipe or a hidden leak.

Why do I have low water pressure in only one faucet?

One weak fixture is a local blockage, not a house problem. The faucet aerator or showerhead is clogged with mineral scale, or the faucet cartridge or the small supply-stop valve under the sink is partly closed or fouled. Unscrew the aerator and soak it in white vinegar for 30 minutes, or swap it for a couple of dollars, before touching anything else.

Can a water heater cause low hot water pressure?

Yes. If cold pressure is fine but hot is weak at multiple fixtures, sediment in the tank or a clogged heat trap or shutoff at the water heater is the usual cause. Flushing the tank clears sediment. A single faucet weak only on hot is almost always the aerator or the hot side of that faucet, not the heater.

How much does it cost to fix low water pressure?

It depends on the cause. Cleaning an aerator is free to a few dollars. A new pressure-reducing valve installed by a plumber often runs $250 to $400. Finding and repairing a hidden leak runs $150 to $500 or more. Repiping corroded galvanized lines is the big one, often several thousand dollars depending on home size and access.

Last reviewed: August 2026.