Start with where it happens

  • IfOnly one faucet or shower head is weakThenCheck its aerator or shower head for scale, then the cartridge and angle stops.
  • IfOnly hot water is weak, everywhereThenLook at the water heater: a partly closed inlet valve, sediment or corroded heater nipples.
  • IfThe whole house dropped suddenlyThenCheck that the main shutoff is fully open, then ask neighbors or your water provider about a supply issue.
  • IfThe whole house has slowly gotten worse over yearsThenSuspect narrowed galvanized pipe or a failing pressure regulator.
  • IfPressure is weak and the meter moves with everything offThenA leak may be stealing pressure; see the hidden leak guide.

Simple checks you can do

  • Unscrew the faucet aerator and rinse out grit and scale, or soak it in vinegar.
  • Soak a removable shower head in vinegar to dissolve mineral deposits.
  • Confirm both angle stops under a weak sink are fully open.
  • Make sure the main shutoff valve is fully open after any recent work.
  • Check whether the problem is only at an outdoor hose bib, which can point to an irrigation or bib valve issue.

Terms you may hear

Pressure regulator (PRV)
A bell-shaped valve near where the main enters the house that reduces street pressure to a safe level. When it fails it can cause low or excessively high pressure.
Static pressure
Pressure measured with no water running, usually with a gauge on a hose bib.
Flow
How much water actually reaches a fixture. Narrowed pipe can show normal static pressure but poor flow.
Aerator
The screen at the tip of a faucet spout that shapes the stream and catches debris.

How a plumber diagnoses it

  1. Measure

    A gauge on a hose bib reads static pressure; a second reading with fixtures running shows how much it drops.

  2. Check the regulator

    If the home has a PRV, its output is compared with what it should be.

  3. Inspect valves

    The main shutoff, water heater valves and stops are checked for partial closure or internal failure.

  4. Look at the pipe

    Pipe material is identified; galvanized lines may be opened at a joint to see how much the inside has narrowed.

The galvanized pipe question

In homes with original galvanized steel supply lines, rust and mineral deposits slowly close up the inside of the pipe. No amount of aerator cleaning will help once that happens. The fix is replacing the affected pipe, either in sections or through a whole-house repipe.

Before agreeing to a repipe for low pressure, ask the plumber to show how they ruled out a regulator or valve problem. Those are much smaller repairs.

Questions to ask

  1. What static pressure did you measure, and what does that tell you?
  2. Is there a pressure regulator, and is it working?
  3. Is the problem the pipe itself, and how do you know?
  4. Would replacing one section help, or does the whole system need attention?

Common questions

Can water pressure be too high?

Yes. Excessive pressure strains valves, supply lines and appliances. A plumber can measure it and check whether a regulator is needed or failing.

Why is only my hot water weak?

The water heater is the common point for all hot water. Sediment, a partly closed valve or corroded fittings at the heater are frequent causes.

Who do I call if the whole street has low pressure?

Contact the water provider listed on your bill. A neighborhood-wide drop is usually a supply issue, not your plumbing.

General information for La Palma, not a quote or professional advice. In an emergency, call 911.