The short answer
Ask two questions. Is it one fixture or the whole house? One fixture is almost always a clogged aerator, cartridge or supply valve — a ten-minute fix. Is it hot water only? Then the problem is at the water heater, usually sediment or a failing dip tube. If it is every fixture, hot and cold, the causes in order of likelihood are a half-closed main valve, a failed pressure-reducing valve, a clogged whole-house filter, corroded galvanized pipe, or a leak. A $12 gauge on an outside spigot tells you whether you have a pressure problem or a flow problem.
Two questions that narrow it down
Before touching anything, walk the house. Run the kitchen sink, a bathroom sink, the tub and an outside spigot, hot and cold separately. Note which are weak. That map does most of the diagnosis:
| Pattern | Where the problem is |
|---|---|
| One faucet or shower, hot and cold both weak | That fixture: aerator, cartridge, or its shut-off valve |
| Hot side weak everywhere, cold fine | Water heater or the hot-side shut-off |
| Everything weak, always has been | Undersized or corroded supply pipe, or a regulator set low |
| Everything weak, started recently | Main valve, failed regulator, clogged filter, or a leak |
| Weak only when something else runs | Flow problem, not pressure: pipe size or a partial blockage |
| Upstairs weak, downstairs fine | Low supply pressure; each floor costs about 4 psi |
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One fixture: aerator, cartridge, supply valve
- Aerator. Unscrew the tip of the faucet, rinse the screen and soak the parts in vinegar for an hour. Mineral scale from North Shore water clogs these every year or two.
- Shower head. Same treatment; many unscrew by hand. Check for a flow-restrictor disc that has clogged.
- Cartridge. A single-handle faucet or shower valve with weak flow after cleaning the aerator usually has a scaled or worn cartridge. It is a brand-specific part; bring the old one to the store or call us with the make.
- Supply valve. The small shut-off under the sink or behind the toilet may not be fully open, or an old multi-turn valve may have failed internally. Open it fully; if that changes nothing, the valve is due for replacement.
Hot water only: the water heater
When cold pressure is fine and hot is weak everywhere, look at the heater. The common culprits are sediment filling the bottom of the tank and choking the outlet, a collapsed dip tube shedding plastic bits into the hot lines (you will find white flakes in aerators), a hot-side shut-off valve that is partly closed, or scale on a tankless heat exchanger. Flushing a tank and descaling a tankless unit are maintenance items; a dip tube is a repair; a tank that is 10+ years old with heavy sediment is usually a replacement — see what that costs in Massachusetts.
Whole house: main valve, regulator, pipes, leak
- Main shut-off valve. Find it where the water line enters the basement. Gate valves (round handle) should be turned fully counter-clockwise; ball valves (lever) fully in line with the pipe. A valve left half-open after utility or meter work is the number-one "sudden drop" cause we find.
- Pressure-reducing valve (regulator). The bell-shaped brass fitting near the meter. They fail after 10–15 years, either dropping pressure or letting it creep up. Adjusting the screw on top may help temporarily; replacement is $250–$500.
- Whole-house filter or softener. A clogged cartridge starves the whole house. Change it. If a softener is in bypass or its resin is fouled, pressure suffers too.
- Galvanized steel pipe. In homes built before about 1960, corrosion narrows the pipe from the inside over decades. Pressure at the meter is fine, flow at the fixtures is not. The fix is repiping in copper or PEX, usually done in sections starting with the worst runs.
- A leak. A significant leak — a split underground service line, a failed pipe in a wall — drops pressure and shows up as a meter that spins with every fixture off. Shut everything, watch the meter for two minutes, and call if it moves. Our leak detection finds it without opening walls at random.
- Municipal supply. Ask a neighbor. A town-side main break or hydrant flushing drops pressure for the whole street, and there is nothing to fix in your house.
How to measure your pressure
A water pressure gauge with a hose thread costs about $12. Screw it onto an outside spigot or the laundry faucet, open the valve fully with nothing else running, and read it. 40–60 psi is normal. Under 40 with a regulator on the line means the regulator is set low or failing; under 40 with no regulator means the street pressure is low or the service line is restricted. Over 80 psi is a code issue that damages fixtures and shortens water heater life — that also gets a regulator.
Now run a second fixture and watch the gauge. If the reading is fine at rest but falls hard under flow, the pressure is there and the flow is restricted — pipe size, corrosion, a partially closed valve or a clogged filter.
When to call
Call when the whole house is affected and the main valve, filter and neighbor check have not explained it; when the meter moves with everything off; when the pressure is over 80 psi; or when you have galvanized pipe and the pressure has been fading for years. Precision Plumbing Solutions diagnoses and fixes water pressure problems across Lynnfield, the North Shore and Greater Boston — pipe repair and repiping, leak detection, regulators and filtration. Call (978) 317-1244 and describe the pattern from the table above; that alone usually tells us what we will find.
Questions people ask
What is normal water pressure for a house?
40 to 60 psi is the comfortable range. Below 40 feels weak; above 80 is over the code limit and hard on fixtures and the water heater, which is why a pressure-reducing valve is installed on many homes.
Why did my water pressure drop suddenly?
A sudden whole-house drop usually means a failed pressure regulator, a partly closed main valve after utility work, a municipal supply problem (ask a neighbor), or a burst or major leak somewhere on your side of the meter.
Can old pipes cause low water pressure?
Yes. Galvanized steel pipe, common in pre-1960s Massachusetts homes, corrodes from the inside until a 3/4-inch pipe has a pencil-width opening. It shows up as pressure that has faded over years, worst at the fixtures furthest from the meter.
Does a water filter reduce water pressure?
A clogged sediment or whole-house filter cartridge is a very common cause of gradual whole-house pressure loss. Changing the cartridge takes five minutes and is worth doing before anything else.
