If pressure dropped at every fixture at once rather than at one tap, the problem is upstream of the fixtures — it is the supply pipe, the pressure regulator, or the meter. In a house with galvanized steel supply, it is almost always the pipe: it corrodes from the inside, so it looks perfectly sound while the bore closes up.

The tell is that the outside of the pipe gives you nothing. A galvanized line can look clean and dry on the basement ceiling while the inside diameter has gone from three quarters of an inch to a straw. Nothing leaks. Pressure just quietly falls off over years, which is why most people do not notice until a second bathroom gets used at the same time.

Confirm it is the supply pipe and not something else

Four things cause house-wide pressure loss. Work through them in this order, because they get more expensive as you go.

• The main shutoff is partly closed. Someone worked on the plumbing and never opened the valve fully. Free to check, and it happens more often than you would think.
• The pressure regulator has failed. Most houses built after about 1960 have one where the supply enters. They last roughly ten to fifteen years and fail closed as often as open.
• The municipal supply changed. Ring your water utility and ask. If the whole street lost pressure, it is not your pipe.
• The supply pipe has corroded closed. The likeliest answer in a pre-1940 house that has never been repiped.

The companion sign that points hard at galvanized pipe is rust-coloured water on the first draw of the morning that clears after ten or fifteen seconds. That is scale shedding off the inside wall of the pipe overnight. Clear water throughout points at the regulator instead.

Two checks you can run yourself

Both take about ten minutes and need one tool that costs less than a takeaway.

• Measure the static pressure. A screw-on pressure gauge costs about $10 to $15 at any hardware shop. Thread it onto an outside hose bib, turn nothing else on in the house, and open the tap. Healthy is 45 to 80 psi. Below 40 confirms you have a real supply problem rather than a fixture problem.
• Compare pressure to flow. Leave the gauge on and have someone open two taps inside. If the reading holds steady, your pressure is fine and you have a volume restriction — a closed-up pipe. If the reading was low to begin with and stays low, look at the regulator first.

If the gauge reads healthy and only one tap is weak, you are in the wrong place — see one fixture slow, the rest fine instead. That is an aerator or a supply stop, and it is a fifteen-minute job you should not be paying anyone for.

What it costs

Ranges below are a guide for judging a quote, not a quote. Access drives the number more than materials do — a slab house with finished ceilings costs far more than a house with an open basement.

• Pressure gauge, do it yourself: $10 to $15
• Pressure regulator replacement: roughly $350 to $700 fitted
• Whole-house repipe in PEX: roughly $4,000 to $12,000 depending on size and access
• Whole-house repipe in copper: typically 30 to 40 percent above the PEX figure

The one thing worth refusing is a partial repipe sold as a fix. Replacing the accessible run near the meter while leaving corroded branch lines behind the walls moves the restriction rather than removing it, and you pay twice. If you are weighing materials, see PEX vs copper repipe.

How urgent is this

Not urgent on its own. Closing-up galvanized pipe is a slow failure and low pressure is an inconvenience rather than a hazard. Plan it, do not panic-buy it, and get three quotes.

It becomes urgent if you also see damp on the ceiling below a bathroom, a jump in the water bill with nothing visible, or pressure that drops away entirely rather than being merely weak. Those are leak signs, and a leak inside a wall is a different and faster-moving problem.

Related

• Rusty water only on the first draw — the companion sign that confirms galvanized pipe
• One fixture slow, the rest fine — if it turns out not to be house-wide
• Copper at the meter, galvanized behind the wall — why a partial repipe fooled you
• What supply pipe is in your walls? — identify it by build decade
• Every drain in the house is slow — the drain-side equivalent of this problem

Back to Plumbing.

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Written by Jaylan Jones. iLikeTo Fix earns a referral fee when a call connects to a contractor. See our business-model disclosure.