Low water pressure in your house: the usual causes

First figure out if it’s one fixture or the whole house. Weak water at a single faucet or shower is almost always something at that fixture, like a clogged aerator or a stop valve that isn’t all the way open. Weak water everywhere points to the main shutoff, a pressure-reducing valve, old pipe, a leak, or a problem on the utility’s side. A cheap pressure gauge on an outside spigot will tell you a lot in about two minutes.

Is it one fixture or the whole house?

Walk the house and turn on the cold water at the kitchen sink, a bathroom sink, a tub, and an outside spigot. Then try the hot at each one.

One weak spot means the problem lives at that fixture. If everything’s weak, look at the supply coming into the house, and if it’s only the hot side, the water heater is the first suspect.

One faucet or shower is weak

Start with the cheap stuff. It’s usually one of these:

• A clogged aerator. That’s the little screen on the tip of the faucet. Unscrew it, rinse out the grit, and soak it in white vinegar if it’s crusted with white scale. Debris often shows up right after the water’s been shut off for a repair.
• A scaled-up showerhead. Tie a bag of vinegar around it overnight, then scrub the nozzles. Hard water scale builds up faster than people expect. We wrote more about that in what hard water does to your plumbing.
• A stop valve that’s partly closed. Check the little valves under the sink or behind the toilet. Somebody may have turned one down during a repair and never opened it back up. Turn it counterclockwise until it stops. If it’s old and stiff, don’t crank on it hard. Old valves like to start leaking at the stem.
• A worn cartridge. Single-handle faucets and a lot of showers use a cartridge inside the valve. When one gets clogged or starts failing, flow drops even with a clean aerator. Swapping one is doable if you’re handy, but you have to shut the water off and match the exact part.

The whole house has weak pressure

Now you’re looking at where the water comes in.

Start with the main shutoff. If anyone’s worked on the plumbing recently, make sure the main valve got opened all the way afterward. A gate valve (round handle) should be turned fully counterclockwise. A ball valve (lever handle) should sit parallel with the pipe.

Next is the pressure-reducing valve. Some houses have a bell-shaped brass valve near where the main line enters. It knocks street pressure down to something your pipes can live with. These wear out, and when they do, pressure can drop off or creep up too high. Adjusting or replacing one is usually a job for a plumber.

Then there’s the pipe itself. In older homes, galvanized steel water pipe rusts from the inside and slowly narrows. Pressure that’s crept down over the years is the classic sign. More on that in our post on galvanized pipes in older homes.

A leak can do it too. Water leaking out somewhere is water that isn’t getting to your shower. Watch for a wet spot in the yard, a meter that spins with everything off, or a water bill that jumped. Here’s how to check for a hidden leak.

And sometimes it’s the utility. Ask a neighbor if their pressure is off too. If it is, call your water utility. They may be working on a main or dealing with a break. In Huntsville, the utility’s side ends at the meter. The line from the meter to your house belongs to you, so a problem there is yours to fix. Other cities are usually similar, but check with your utility.

Only the hot water is weak

Look at the water heater first. There’s a shutoff valve on the cold line going into the top of it. Make sure it’s fully open.

If it is, sediment is the next suspect. Minerals settle in the tank and can break loose and clog the hot side of faucets and valves. Tankless heaters have a small inlet screen that clogs, and scale can build up inside the unit itself. Flushing helps in both cases.

How to check your water pressure

Any hardware store sells a pressure gauge that screws onto a hose spigot. It’s cheap and worth keeping in the garage.

1. Turn off anything that’s using water, like the washer, dishwasher, and sprinklers.
2. Screw the gauge onto the outside spigot closest to where the water line comes in. Hand-tight is fine.
3. Open the spigot all the way and read the needle.
4. If you can, check again at a different time of day. Pressure can dip during busy morning hours.

A lot of homes sit somewhere around 40 to 80 psi. If you’re well below that, you’ll feel it in every shower. Above about 80 psi, a pressure-reducing valve is generally recommended, because high pressure is hard on water heaters, toilet fill valves, supply lines, and faucets.

The reading also tells you where to look. A good number at the spigot with a weak shower inside means the problem is inside the house. A low number at the spigot points back toward the main, the valve, the service line, or the utility.

Call a plumber if you see this. Pressure that dropped suddenly along with the sound of running water, a soggy patch in the yard, or a gauge reading well over 80 psi.

If you’ve cleaned the aerator, opened every valve, and the gauge still says something’s off, give us a call.