Low Water Pressure: One Fixture or the Whole House?

The first question with low water pressure is not what is wrong but where. A single slow fixture is almost always a small, cheap problem, frequently one you can fix yourself in twenty minutes. Pressure that has dropped across the entire house points somewhere else entirely.

Sorting that out before calling anyone saves money, because the two problems have almost nothing in common.

Start With the Test

Run the cold water at several fixtures in turn: kitchen, each bathroom sink, each shower, the outside hose bibb. Note which are weak and whether it affects hot, cold or both.

Three patterns emerge, and each points somewhere different.

One Fixture Only

This is the common case, and in Las Vegas it is usually mineral scale.

Aerator. The screen on the end of a faucet catches scale and grit. Unscrew it, and you will typically find it partly blocked with white deposit. Soak it in vinegar, rinse, reinstall. This single step resolves a large share of "my kitchen faucet is slow" calls.

Shower head. The same problem, same fix. Scale blocks the nozzles unevenly, which is why the spray goes crooked before it goes weak.

Angle stop. The small shutoff valve under a sink or behind a toilet. These seize partly open, particularly if they have not been turned in a decade.

Cartridge. If a single shower or faucet is weak on hot only, or on both after a repair elsewhere, the cartridge may be scaled or damaged. That is a fixture repair rather than a plumbing-system problem.

If cleaning the aerator and shower head fixes it, you are done.

Hot Water Only, Everywhere

Weak hot water throughout the house with normal cold points at the water heater. Sediment buildup is the usual cause here, and it comes with the other symptoms covered in our post on why valley water heaters fail early: popping noises, hot water running out sooner, a gas bill creeping upward.

A scaled-up heater and a scaled-up house often arrive together, because the cause is the same.

The Whole House

Every fixture weak, hot and cold, is a supply-side problem. Several possibilities, in rough order of likelihood.

Pressure reducing valve. Most valley homes have a PRV near the main shutoff, and they wear out, typically after eight to fifteen years. They can fail in either direction: stuck low gives you weak pressure everywhere, stuck high gives you the far more destructive problem covered in our post on high water pressure. A plumber tests with a gauge and replaces the valve.

A partly closed valve. Worth ruling out before anything else. The main shutoff or a meter valve left partly closed after previous work is not a rare finding, and it costs nothing to check.

Corroded galvanized pipe. In older homes, rust builds inward and narrows the bore throughout the system. Pressure decline here is gradual over years rather than sudden, and it is usually accompanied by discolored water on first draw. That is a repiping conversation rather than a repair.

A hidden leak. A significant leak between the meter and the house drops pressure and wastes water continuously. The check is simple: turn off every fixture in the house, then watch the meter. If it is still moving, water is going somewhere. That is where leak detection comes in, and if the line runs under the slab, our post on slab leak signs is the relevant read.

Utility-side work. Occasionally the cause is upstream. If neighbors report the same thing, it is worth checking with the water district before paying anyone to investigate your house.

The Pressure Number Itself

A gauge on an outside hose bibb costs very little and answers the question directly. Normal residential pressure sits roughly between 40 and 80 psi. Below about 40 is genuinely low. Above 80 is high enough to be damaging fixtures and appliances continuously, which is worth knowing even when nothing has failed yet.

Test in the evening when demand is lower, and take a second reading in the morning, because supply pressure varies through the day.

When to Call

Call when cleaning the aerators has made no difference and the problem covers the whole house, when pressure has dropped suddenly rather than gradually, when the meter is moving with everything off, or when there is discolored water alongside the pressure loss.

Sudden loss across the house, especially with any sound of running water, is worth treating with some urgency rather than monitoring.

Practical Takeaways

Locate the problem before diagnosing it. Clean the aerator and shower head first, because in this valley that is the answer more often than not. Hot-only points at the heater. Whole-house points at the PRV, a valve, corroded pipe or a leak. A ten-dollar pressure gauge answers in two minutes what would otherwise be guesswork.

Talk to a Licensed Plumber

American Brothers Plumbing handles leak detection and fixture repair across Las Vegas, Henderson, Summerlin and the surrounding valley. Call (702) 704-1776 for a free upfront estimate.