Pressure, flow and why the difference matters
Pressure is how hard water pushes; flow is how much arrives. A house can have normal pressure at the hose bib and still get a weak shower because scale or corrosion is choking the pipe or the fixture. Knowing which you have points to the cause.
Many homes also have a pressure-reducing valve, or regulator, near where the main enters the house. It protects fixtures from high street pressure, but regulators wear out. A failing one can let pressure drop, or swing too high, which is just as much of a problem.
Work from the fixture back to the street
- Is it one fixture or all of them?.If only one faucet or shower is weak, unscrew the aerator or showerhead and look for scale and grit. Hard water often clogs these first.
- Hot side, cold side, or both?.Weak hot water alone points toward the water heater, its connectors or its shutoff valve.
- Check the main shutoff.Make sure the main valve is fully open. Old gate valves can partly close or fail internally.
- Test the house pressure.An inexpensive gauge on a hose bib shows static pressure. Compare it with what a plumber considers normal for a home.
- Look at the regulator and service line.If pressure is low at the hose bib nearest the main, the regulator, the service line from the meter, or the supply from the street may be the cause.
Common causes and fixes
| Cause | Clue | Typical fix |
|---|---|---|
| Clogged aerator or showerhead | One fixture weak, others fine | Clean or replace the aerator or head. |
| Failing pressure regulator | Whole house low or fluctuating | Adjust or replace the regulator. |
| Corroded galvanized pipe | Gradual decline over years, brown water | Replace sections or repipe. |
| Partly closed or failed valve | Low after recent plumbing work | Open fully or replace the valve. |
| Leak on the service line | Low pressure plus meter moving with the house off | Repair or replace the line from meter to house. |
| Supply issue in the street | Neighbors affected too | Contact the water provider on your bill. |
Repairing versus replacing the service line
Spot repair
- Fixes a single leak or damaged section.
- Smaller excavation.
- Leaves the rest of an old line in place.
Full replacement
- New line from the meter to the house.
- Can be trenched or, in some cases, pulled through with trenchless methods.
- Often paired with a new main shutoff valve and regulator.
Questions to ask a plumber about pressure
- What is my static pressure at the hose bib, and is it in a normal range?
- Do I have a pressure regulator, and is it working?
- Is the service line from the meter galvanized, copper or plastic?
- Would replacing the main shutoff valve help?
- Does service line replacement need a permit? Check with the city.
Common questions
Can water pressure be too high?
Yes. High pressure wears out faucets, toilet valves, hoses and water heaters faster. A working regulator keeps it in a safer range.
Why did pressure drop after a plumbing repair?
Debris dislodged during the work often collects in aerators and valves. Cleaning them usually restores flow.
Is low pressure a sign of a leak?
It can be, especially if the meter moves with everything off. Run the meter test to check.
General information for La Mirada, not a quote or professional advice. In an emergency, call 911.