The number, and how to get it
A pressure gauge that screws onto an outdoor hose bib costs very little. Take the reading with nothing else running.
50-75 psi is the healthy range. Above 80 psi you are outside what most fixtures, flexible supply lines and appliance inlet valves are designed for, and many manufacturers' warranties say so explicitly.
It is worth taking a reading at night as well as during the day. Municipal pressure is often higher overnight when demand across the system drops, and a house that reads an acceptable 78 psi at 6pm can be sitting at 95 psi at 3am — which is when nobody is watching and washing machine hoses fail.
That overnight figure is the one that determines what your plumbing actually endures.
The four signs
None of them announce themselves as a pressure problem, which is the difficulty.
- Banging or knocking when a tap or appliance shuts off. Water hammer — moving water stopped abruptly, and the shock has to go somewhere. High pressure makes it far worse because the water is moving faster to begin with.
- Faucets that drip again soon after being repaired. A new washer or cartridge sealing against excessive pressure fails early. If a repair does not hold, suspect the pressure rather than the part.
- Appliances failing before their time. Dishwasher and washing machine inlet valves, ice makers, and water heaters all take the strain continuously. Two or three early failures in a few years is a pattern, not luck.
- The water heater's relief valve discharging. The T&P valve opens on excess temperature or pressure. If it weeps periodically, it is reporting something real.
Worth knowing
The most consequential thing high pressure does is to the flexible braided supply lines behind toilets and under sinks, and the rubber hoses on a washing machine. Those are the components that fail as a burst rather than a drip — and they are usually behind something, unattended.
What causes it
A failed pressure-reducing valve. Most homes here have one near the main shutoff, reducing municipal supply to a domestic level. They last 10-20 years and then drift — often downward, sometimes upward, occasionally failing open so the house sees full main pressure. This is the most common cause and it is a contained replacement.
Municipal supply. Pressure varies with elevation and distance from the pumping station, and a house lower in the system sees more. Nothing to be done at the source; the answer is a regulator on your side.
Thermal expansion in a closed system. Slightly different — this produces pressure spikes rather than constant high pressure. Water expands as the heater warms it, and if there is a check valve or regulator on the incoming main, that expansion has nowhere to go. Pressure climbs until something relieves it. The fix is an expansion tank, not a bigger relief valve.
Why it matters more than low pressure
Low pressure is annoying and obvious, and it gets fixed because people complain about it.
High pressure is comfortable and invisible, and it shortens the life of every valve, seal, hose and appliance connection in the house simultaneously. The cost does not arrive as a plumbing bill — it arrives as a dishwasher, then a washing machine, then a water heater, spread over years and never attributed to the actual cause.
And the failure mode is worse. A low-pressure problem inconveniences you. A high-pressure problem eventually bursts a supply line while everyone is out.
A regulator is one of the cheapest components in a plumbing system. Replacing one that has drifted is straightforward, and it protects everything downstream of it.
Worth doing while you are at it
If the pressure is high, replace the rubber washing machine hoses with braided stainless ones. Rubber hoses are the single most common cause of domestic water damage, they are inexpensive, and high pressure is exactly what finishes them.
Check the T&P discharge pipe at the water heater for mineral crusting, which is the residue left by intermittent discharge. It is evidence of a pressure problem even if you have never seen it happen.
And once a regulator is fitted or replaced, take a gauge reading again — including overnight. Regulators are adjustable, and it is worth confirming where yours has actually been set rather than assuming.