Why Is My Water Pressure Low? (And How to Fix It)
Low water pressure has 7 common causes, most fixable in 15 minutes without a plumber. Work through them in order, easiest first; the aerator is the cause 60% of the time.
Quick answer: Low water pressure has seven causes. First identify whether it’s one fixture or whole-house. For a single faucet or shower, unscrew the aerator or shower head and soak in vinegar overnight to dissolve calcium buildup, this fixes 60% of cases. Check fixture shut-off valves are fully open. For whole-house low pressure, check the main shut-off and pressure regulator where water enters the home (7-12 year lifespan). Hot-water-only low pressure means sediment in the water heater, flush it.
Standing in a sad, dribbling shower is frustrating, especially if it used to be fine. Most low-pressure causes are something you can identify and fix in 15 minutes. Figuring out which of seven possible causes you have is the only hard part, and most of those checks take 30 seconds.
Our master shower lost pressure over a couple of weeks last summer until it felt like standing in a heavy mist. I spent five minutes unscrewing the shower head, soaking it in vinegar in a bag overnight (the rubber-band-the-bag-onto-the-arm trick), and brushing the calcium out of the rim holes with a toothbrush. Next morning the spray was back to normal. Aerator and shower-head clogs are the cause for the majority of cases. Whole-house pressure problems are real but rarer.
Below: each cause in order from most common to least common, so you can methodically eliminate them.
What You’ll Need
Most of the diagnosis requires nothing. The actual fixes (if needed) use:
- A bucket
- Channel-lock pliers
- White vinegar
- A small toothbrush or old toothbrush
- A flashlight
- A pressure gauge (~$10 at any hardware store, optional but useful)
Step 1: Is It One Fixture or Whole-House?
The first thing to figure out. It changes everything.
Test: Turn on the hot water at the kitchen sink, bathroom sink, shower, and bathtub one at a time. Note which ones have low pressure and which are normal. Then do the same for cold.
- One fixture only: clogged aerator, clogged shower head, partially closed shut-off valve, or a problem with that fixture specifically. Skip to Step 3.
- Multiple fixtures, only hot or only cold: problem with the water heater (for hot) or main shut-off valve (for cold).
- All fixtures, hot and cold: issue with your home’s main water supply, main shut-off, pressure regulator, or municipal supply.
Step 2: Check the Easy Stuff First
Before tearing into anything, rule out the obvious:
- Is the main shut-off valve fully open? Usually in the basement, garage, or crawl space, where your water enters the house. Look for a lever or wheel valve. Turn it fully counterclockwise (open). If it’s a quarter-turn ball valve, the handle should be parallel to the pipe.
- Did you recently have plumbing work done? Plumbers sometimes leave a shut-off partially closed by accident.
- Are you on a well? Low pressure could mean a failing pressure tank or a problem with the well pump. Different category of fix.
- Did the city do work on your street? Municipal repairs sometimes temporarily reduce pressure. Check your local water authority’s outage notices.
Step 3: Clean the Aerator (Single Fixture, Low Pressure)
The #1 cause of low pressure at a single faucet. The aerator is the little screen at the tip of the spout. It catches debris from your water supply, and over months and years, mineral buildup (especially calcium and lime) clogs it shut.
Steps:
- Unscrew the aerator by turning it counterclockwise. Channel-lock pliers if it’s stuck, but wrap a rag around it first to avoid scratching the chrome.
- Run water through the faucet without the aerator. Is the pressure full? If yes, the aerator is your problem.
- Soak the aerator in white vinegar for 30 minutes to dissolve mineral buildup.
- Scrub it with an old toothbrush.
- Rinse and reinstall. Hand-tight.
Five-minute fix. Do this every six months and you’ll never have aerator problems.
Step 4: Clean the Shower Head
Same principle, slightly different mechanism. Mineral buildup clogs the small holes on a shower head, dropping flow.
Steps:
- Unscrew the shower head from the arm coming out of the wall. Counterclockwise. Pliers if stuck (wrap a rag around it).
- Soak it in white vinegar overnight, or fill a plastic bag with vinegar and rubber-band it onto the shower arm so the head is fully submerged.
- Rinse and use a small brush or toothpick to clear any remaining clogged holes.
- Reinstall. Wrap fresh plumber’s tape on the threads before screwing it back on.
For some shower heads, especially newer water-saving ones, there’s a small flow restrictor disc inside. It’s there to limit gallons-per-minute. You can remove it (but check your local code first, some jurisdictions require it).
Step 5: Check the Shut-Off Valves at the Fixture
Each sink, toilet, and shower has shut-off valves where the supply lines connect. Sometimes they get bumped partially closed, or seize from disuse, restricting flow.
Steps:
- Locate the shut-off valves under or behind the affected fixture.
- Open them fully, turn counterclockwise until they stop.
- Test the fixture.
If a shut-off valve is stuck, gently work it back and forth. If it won’t fully open, it likely needs replacement (a $5 part, 15-minute job).
Step 6: Check Your Pressure Regulator (Whole-House Low Pressure)
If pressure is low everywhere in the house, you may have a failing pressure regulator. The regulator is a bell-shaped brass fitting on the main water line where it enters the house, sometimes inside, sometimes outside.
Pressure regulators have a typical lifespan of 7-12 years. As they wear, they often fail by dropping the regulated pressure too low (or, occasionally, by letting full city pressure through, which is much worse).
Test with a pressure gauge:
- Screw the pressure gauge onto an outdoor spigot or hose bib.
- Open the spigot fully.
- Read the gauge. Normal residential pressure is 45-80 psi. Below 40 psi = low.
If pressure is low at the gauge, your regulator is suspect. Most pressure regulators have an adjustment screw on top, you can turn it clockwise (a quarter turn at a time) to raise pressure. If the screw maxes out and pressure is still low, the regulator needs replacement. A job many DIYers handle, but it requires shutting off the main water, call a plumber if you’re not confident.
Step 7: Sediment in the Water Heater (Hot Water Only)
If only your hot water has low pressure, sediment buildup in the water heater is the most common cause. Over time, minerals from the water settle to the bottom of the tank and start blocking the outlet.
Flush the water heater:
- Turn off the water heater (gas: turn the dial to “pilot”; electric: shut off the breaker).
- Close the cold water supply valve to the heater.
- Attach a garden hose to the drain valve at the bottom and run it to a floor drain or outside.
- Open the drain valve and let the tank drain.
- Open the cold supply for a moment to flush out residual sediment.
- Close the drain, close the hose connection, open the cold supply, and run a faucet upstairs to let air escape as the tank refills.
- Restore power/gas to the heater.
Flushing your water heater once a year is good preventive maintenance.
Step 8: Hidden Leak (Less Common)
If pressure is low everywhere and you’ve ruled out the above, you may have a hidden leak somewhere in the system. Look for:
- Water staining on ceilings, walls, or floors
- Hissing sounds near walls
- Higher-than-usual water bills
- A wet spot in the yard near where the main line enters the house
A hidden leak is one of the few diagnoses that genuinely warrants a plumber, they have tools (acoustic listeners, infrared) that locate leaks without tearing open walls.
Common Mistakes to Avoid
Skipping the aerator. People often assume low pressure is a pipe issue and start considering expensive repairs. The aerator is the cause 60% of the time. Always check it first.
Mistaking flow restrictors for clogs. A modern shower head limited to 2.5 GPM by a flow restrictor isn’t “broken”, it’s working as designed. Compare to your old shower head before deciding it’s clogged.
Cranking the pressure regulator wide open. Most home plumbing is rated for 80 psi max. Setting your regulator above that can rupture supply lines and damage appliances. If your regulator screw is maxed and pressure is still low, the regulator is broken, don’t try to force it.
Ignoring the hot-water-only clue. If only hot is weak, the cause is in the water heater, not the pipes. Don’t chase the wrong issue.
Confusing the meter valve with the house shutoff. Most homes have two separate shutoffs on the main line: one at the water meter near the curb (operated by your utility) and one at the point where water enters the house (yours to control). If the house shutoff is fully open but pressure is still low across every fixture, the meter-side valve may be partially closed, especially after city work on the street. A $10 pressure gauge on an outdoor spigot confirms it quickly: below 40 psi on that test means the problem is upstream of your house shutoff.
Frequently Asked Questions
What’s normal residential water pressure? 45-80 psi. Below 40 feels weak. Above 80 stresses pipes and appliances.
Why does my pressure drop when more than one fixture is running? Some pressure drop is normal, you’re splitting flow. But if it drops dramatically (shower drops to a trickle when someone flushes a toilet), that suggests either too-small supply lines or a partially clogged main.
Can hard water cause low pressure? Yes, mineral buildup from hard water is the root cause of aerator clogs, shower head clogs, and water heater sediment. A water softener can prevent the buildup if hard water is severe in your area.
Is low water pressure dangerous? No, just annoying. High water pressure (above 80 psi) is the dangerous one because it stresses pipes and joints.
My toilet fills very slowly but everything else is fine. That’s almost always the fill valve in the toilet, they have small inlet screens that clog with sediment. Five-minute fix from inside the tank.
Pressure dropped right after the city replaced my water meter. Is that related? Almost certainly yes. Water utility crews sometimes leave the curb-side shutoff partially open after a meter swap, it’s a common oversight. Locate the meter box near your property line (usually a small rectangular cover flush with the ground near the curb), open it, and check that the valve is fully open. If you’re not comfortable doing that, call your water utility and ask them to confirm the valve position. It takes them five minutes and costs nothing.
The aerator and shower-head fixes solve more than half of pressure problems. Work through the seven causes in order and you’ll know within an hour whether you need a plumber or a ten-dollar part.