Low Water Pressure? Whole-House vs One-Fixture Causes
The first question settles most of it: is the pressure low everywhere, or only at one fixture? One slow faucet is almost always a clogged aerator or worn cartridge you can clear yourself. A whole-house drop points at the pressure regulator, a partly closed main valve, a hidden leak, or old galvanized pipe. Here is how to read which one you have before anyone quotes a repipe.
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- !Pressure dropped to a trickle suddenly and you hear water running with every fixture off: a hidden leak or main break may be active
- !A wet spot, warm floor area, or sound of running water shows up the same day the pressure fell
- !Your water meter dial keeps spinning after you close every fixture and appliance valve
- !Pressure loss came with discolored or sputtering water and a drop in the street main reported by neighbors
- !You smell sewage or see backflow at a drain while pressure is low: cross-connection risk, stop using the water
- ✓Test one fixture vs all of them: if only the kitchen faucet is weak, the problem is local, not your whole system
- ✓Unscrew the faucet aerator (the screen tip) and rinse out grit and mineral flakes, then reattach and retest
- ✓Pull the showerhead and soak it in vinegar overnight to clear scale, the most common cause of weak shower flow
- ✓Check that the main shutoff and the meter valve are fully open: a handle left half-turned chokes the whole house
- ✓Compare hot vs cold at the same faucet: if only hot is weak, the issue sits at the water heater, not the main line
- →Pressure is low at every fixture and the main valve is confirmed fully open
- →A pressure gauge on a hose bib reads below 40 PSI or you suspect the regulator has failed
- →Hot-side pressure is weak throughout the house and flushing the heater did not restore it
- →The home has original galvanized steel supply lines and flow has dropped over years
- →You cleaned the aerator and cartridge area and a single fixture still runs weak: an internal valve or stop may be clogged
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Start here: one fixture or the whole house
This single split decides whether you reach for a wrench or the phone. Walk the house and open faucets, the shower, and a hose bib. If only one fixture is weak, the cause lives in that fixture and the repair is small. If every tap is down, the problem is upstream at the regulator, the main valve, or the pipes feeding the house.
A third pattern is hot-only: cold runs fine but hot dribbles everywhere. That points at the water heater, not the main supply, and is covered below. And a fourth is sudden: pressure that was fine yesterday and is a trickle today, which usually means a failed part or a leak rather than slow buildup.
Sort your symptom into one of those four buckets before reading on. The fixes and the prices are completely different, and chasing the wrong one wastes a service call.
One fixture weak: aerator, cartridge, or stop
The aerator is the small screen that threads onto the faucet spout. Mineral flakes and pipe debris collect there and choke flow first. Unscrew it by hand or with taped pliers, rinse the screen, and reattach: this clears a large share of one-faucet complaints for nothing.
If the aerator is clean and flow is still weak, the cartridge or the angle stops under the sink are the next suspects. A worn or scaled cartridge restricts a single faucet and runs $100 – $350 to replace depending on the brand and whether it is a kitchen, lavatory, or shower valve. A weak shower specifically is often just scale: see shower head leaking and flow issues for the soak-and-clear routine.
Angle stops (the small shutoff valves under the sink) can clog with debris or never fully open after a repair. Closing and reopening them fully sometimes restores flow on its own.
Whole house weak: PRV, main valve, leak, galvanized
Four causes drop pressure everywhere. First and easiest: a main shutoff or meter valve left half-closed after work. Confirm both are fully open before anything else. Second: the pressure reducing valve (PRV) at the main, which fails gradually and can clamp your whole house down to a trickle. Replacement runs $250 – $600 installed and is covered on our PRV replacement cost page.
Third: a hidden leak bleeding off pressure before it reaches your fixtures. If the meter spins with everything off, you have one, and leak detection locates it without tearing up walls. Fourth, and the slow one: galvanized steel pipe. These lines rust closed from the inside over decades, and by the time pressure suffers, the cure is replacement, not repair. That is a galvanized pipe replacement conversation, sometimes a whole-house repipe.
Hot-only weak, and sudden drops
When only the hot side is weak across the house, the water heater is the choke point. A partly closed shutoff valve on the hot outlet, or scale and sediment narrowing the heater nipples, restricts hot flow while cold stays strong. Confirm the heater shutoff is fully open, then have the tank flushed; persistent hot-only weakness points at scaled fittings that a plumber clears or replaces.
A sudden whole-house drop is its own signal. A PRV can fail closed overnight, a service line can develop a break, or your utility may be working on the street main. Check with neighbors and your water provider first, since a main-side problem is theirs to fix. If the cause is on your side of the meter, a service line break becomes a main water line replacement discussion.
What each fix costs
The repair menu spans from a no-cost rinse to a repipe, and your symptom bucket sets the range. Cleaning an aerator or showerhead: $0 – $20 in vinegar and ten minutes. Replacing a faucet or shower cartridge: $100 – $350 installed. A new pressure reducing valve: $250 – $600 installed, and it usually also fixes pressure that swings too high, which protects the rest of your fixtures.
The bigger numbers come from pipe condition. If galvanized lines have rusted closed, partial or whole-house replacement is the only durable fix; pricing scales with home size and runs into the thousands. A leak repair depends on location, but detection alone is $150 – $400. The takeaway: clean the cheap parts first, gauge your pressure against the normal range for a house, and let that reading decide whether you are facing a $15 fix or a pipe conversation.
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