Find the cause in four quick checks
Do these in order. Each takes a few minutes and needs no tools beyond a wrench or pliers.
- 1
Compare hot and cold
If only hot water is weak, the problem is the water heater, its valves, or hot-side pipes. If both are weak, keep going.
- 2
Check one tap at a time
Unscrew the aerator from the weak faucet. If flow jumps, the aerator was full of grit or scale.
- 3
Check the main valve
Find where water enters the house and confirm the valve is fully open. A gate valve stuck half open is common.
- 4
Ask the neighbors
If the street is affected, the issue is outside your walls. If only you are affected, it is inside the house or in your service line.
Write down what you find. A plumber can diagnose far faster with a clear picture of where flow drops.
Symptoms, likely causes and the usual fix
Match what you see to the row. These are the common pairings.
| What you notice | Likely cause | Typical next step |
|---|---|---|
| One faucet is weak | Clogged aerator or cartridge | Clean or replace the aerator or cartridge |
| Every tap weak, house-wide | Main valve partly closed or failing regulator | Open valve fully, test the pressure reducing valve |
| Weak on upper floors only | Pressure loss in a long run of narrow pipe | Pressure test, review pipe size |
| Pressure fell slowly over years | Corroded galvanized pipe | Pipe replacement for affected runs |
| Pressure dropped suddenly | Leak, stuck valve, or damaged service line | Shut off, call for diagnosis |
| Weak after city flushing | Sediment in aerators and valves | Clean aerators, run cold water until clear |
A pressure gauge on an outdoor spigot will tell you the static pressure. A plumber can read it and tell you if it is within a normal residential range.
Inside-the-house causes in more detail
Most low pressure complaints end up in one of these.
Aerators and fixtures
Mineral grit, scale from a water heater, and flecks from old pipe collect in small screens. Remove, soak in vinegar, rinse, and refit.
Pressure reducing valve
Many homes have a bell-shaped PRV near the main shutoff. When it wears out, pressure drops or swings. Replacement is a standard plumber job.
Galvanized steel pipe
Older homes may still have galvanized supply lines. Rust builds up on the inside wall and narrows the pipe, so flow shrinks even when pressure at the street is fine.
Hidden leak
A leak between the meter and the house reduces pressure at the taps. If the meter spins with everything off, call for leak detection.
If you suspect galvanized pipe, a plumber can often confirm it at the meter or main with a visual check and a magnet test.
What a plumber checks that you cannot easily check
A plumber starts with a gauge on the house side of the main valve and reads static pressure with nothing running. Then the gauge stays on while a few fixtures open, to see how far the number falls. A small drop means the supply is healthy. A big drop means a restriction between the gauge and the street, or inside the house.
Next comes the pressure reducing valve if the house has one. These valves are adjustable and they wear. Sometimes a simple adjustment brings pressure back, and sometimes the valve needs replacing. The plumber also checks the meter side shutoff, any filter or softener on the line, and the water heater inlet valve.
Only after those steps does it make sense to talk about pipe replacement. Opening walls is the expensive part of a plumbing job, so a pressure test that rules out the cheap causes first saves real money.
Pressure still low after the checks?
Tell dispatch which taps are weak and what you already tried. We will plan the next test so you are not paying for guesses.
Melrose water supply and main flushing
Melrose buys its water from the MWRA. The city's Water and Sewer Division operates two water pump stations and reads about 8,500 water meters. The city also flushes its water mains to clear sediment.
The most recent round, in fall 2025, ran from Monday, September 8, to late October, generally 8 am to 4 pm. The city warned that water may look rusty or cloudy, to run cold water until it clears, and to hold off on hot water, laundry and the dishwasher until then. It also said sediment can clog home pipes, reduce pressure or discolor water. If your pressure dipped during flushing, clean your aerators and check the city's current notices for this year's schedule.
Source type: city website
When the problem is between the street and your meter
If every fixture is weak and the interior valves are open, the line that brings water into your home is the next suspect. Corrosion, partial blockage, a crushed section or a leak can all choke flow without any sign above ground. Our water service line repair team can test flow at the entry point and tell you whether the line, the valve or the meter connection is the weak link.
If the cause is old galvanized supply pipe inside the walls, spot repairs only buy time. A full or partial repiping project replaces the narrowed runs. Older homes often show the same pattern, so a thorough pressure check can save repeated visits. We also serve Wakefield and Malden.
Do not ignore a sudden drop
A sudden pressure loss with a hissing sound, a wet spot, or a spinning water meter with everything off can mean a leak. Shut off the main valve and call right away. Water in a basement, near a panel or in a ceiling is an emergency until proven otherwise.
Questions we hear
Peak demand on the street can reduce pressure when many homes draw water at once. If the dip is regular and lasts, ask your water utility whether other customers on your street see it. If it only happens with one tap, the cause is local to that fixture.
Flushing moves sediment out of the mains. Some of it can reach home plumbing and clog aerators or washing machine screens. Running cold water until it clears and cleaning aerators afterward is the usual cleanup.
Screw a pressure gauge onto an outdoor hose spigot or a laundry sink, close other taps, and read it. Many gauges cost little at hardware stores. A plumber can read the result and tell you whether your home is in a normal residential range.
Yes. A clogged cartridge or undersized filter restricts flow. Change the cartridge first, and if pressure returns, you found the cause.
No. If only hot water is weak, sediment in the tank or a partly closed hot-side valve is more likely. If cold water is also weak, the issue lies upstream of the heater.
Only if the pipes are the restriction. A pressure test and flow check before repiping prevents spending money where the problem is a valve or a regulator.