Why Your Water Pressure Is Wrong, and What Actually Fixes It

Pressure complaints split into two piles, and they have almost nothing to do with each other. Working out which pile you are in takes about a minute and saves you replacing parts that were never the problem.

Start here: is it one fixture or the whole house? Go around and run the taps. If the kitchen sink is feeble but the shower is fine, that is a local fault and it is usually cheap. If everything in the house is weak, or everything is violent, that is a system fault and it is usually the regulator.

One weak fixture is nearly always one of three things. A scaled-up aerator on the end of the tap: unscrew it, and if it is packed with white grit, that is your answer, and our water will do that again in a year. A worn cartridge inside the valve. Or an angle stop under the sink that somebody left half closed years ago and nobody has touched since. None of those is a big job.

In the foothills, it is usually the opposite. Around here, especially up in the foothill pressure zones in Almaden, Santa Teresa, Berryessa and Alum Rock, the more common fault is not too little pressure. It is too much.

High pressure does its damage slowly. It shortens the life of every valve, supply line, toilet fill valve and appliance hose in the building, and you replace them one at a time over several years without ever asking why they keep failing. If you have replaced two toilet fill valves and a washing machine hose in eighteen months, stop replacing parts and put a gauge on it.

That gauge costs less than takeout and screws onto any hose bib. It tells you in ten seconds what the rest of your plumbing is living with. The number you want to see is somewhere in the fifties or sixties. Well up in the eighties or beyond means the pressure regulator on your house has either failed or was never adjusted properly, and everything downstream is paying for it.

The other tell is noise. If pipes bang when the washing machine shuts off, or when the sprinklers cut out, that is water hammer: a column of moving water hitting a valve that closed faster than the water could stop. High pressure makes it worse. A regulator that is doing its job, plus a couple of arrestors in the right places, usually calms the whole system down.

Whole-house low pressure has a shorter list of causes: a regulator that has failed closed, a partly shut main valve, galvanized supply pipe that has rusted closed from the inside, or a leak somewhere between the meter and the house. The galvanized one is common in the older neighborhoods, such as Willow Glen, the Rose Garden and older Campbell, and it cannot be fixed with a fitting. Once a run has closed up it has closed up.

If your supply lines and toilet valves keep failing and you have never had the pressure checked, that is the first thing to do. More on regulators and valves, and on repiping if it turns out the pipe itself is the problem.