Get a number before you get an opinion
A pressure gauge that screws onto any outdoor hose bib costs very little and settles the argument in seconds. It is the first thing off the truck on this call, and it is worth owning one.
Take the reading with nothing else running. Under 40 psi confirms what you are feeling. Between 50 and 75 is normal, and if you land there the complaint is probably flow rather than pressure — a different problem with different causes, usually a restriction rather than a supply issue.
Over 80 psi is worth acting on even though it feels like the opposite of a problem. High pressure shortens the life of every valve, hose and appliance connection in the house, and it is what turns a washing machine hose into a flood.
Worth knowing
Take the reading at a hose bib before the softener if you have one, and again after, if you can. A large drop across the softener points at the softener rather than the supply — a resin bed that has fouled will choke flow noticeably.
Whole house: the pressure regulator, first
Most homes here have a pressure-reducing valve near the main shutoff, and it is the most common cause of whole-house pressure loss simply because it is a wearing part. They generally last 10 to 20 years and then drift — usually downward.
The tell is that the drop happened gradually and affects everything equally, hot and cold alike. Replacement is a contained job and typically resolves it outright.
Worth knowing: a regulator can fail in the other direction too, and a house that suddenly has aggressive pressure everywhere has the same part to blame.
Whole house: the other five causes
If the regulator checks out, these are the rest, roughly in order of how often they turn out to be the answer.
- A partially closed main shutoff. Bumped, or left part-way after previous work, or seized mid-travel. Costs nothing to check and occasionally solves the whole thing.
- Scale narrowing the supply lines. Hard water deposits inside galvanized and older copper over decades, and the internal diameter shrinks. If the house has galvanized supply, this is often well advanced.
- A slab leak. Pressure diverted into the ground. Usually arrives with a rising bill, water audible with everything off, or a warm patch on the floor — see the slab leak signs.
- A municipal issue. Occasionally it is genuinely the city side. Ask a neighbour before paying anyone to investigate.
- Well system trouble. On a well, low pressure usually means the pressure tank, the pressure switch or the pump — not the plumbing in the house at all.
One fixture only: start with the cheapest thing
When one tap is weak and everything else is fine, the problem is at that tap. This is genuinely the good outcome.
The aerator — the screen at the end of the spout — is the most common single-fixture cause in this area, because our water leaves mineral behind and that screen is where it collects. Unscrew it, soak it in vinegar, rinse it, put it back. A showerhead is the same problem with the same fix.
If cleaning the aerator does nothing, the next candidates are the fixture's own shutoff valve under the sink (partially closed, or corroded internally), then a failing cartridge inside the faucet.
One useful distinction: if hot is weak everywhere but cold is fine, that is not a fixture problem. That points at the water heater — scale at the outlet, or a failing dip tube.
What we actually do on this call
Gauge on the hose bib for a baseline. Then hot versus cold, then fixture by fixture, working from the meter inward — each step rules out everything upstream of it.
That sequence usually places the cause in well under half an hour, and it matters because the answers here range from a five-minute aerator clean to a whole-house repipe. Nobody should be quoting the second before they have ruled out the first.
If the reading comes back high rather than low, we will say so, because that is the version of this problem that quietly costs you appliances.