Low pressure at one faucet is usually a clogged aerator or a fixture problem. Low pressure everywhere is different. It means something is restricting water before it reaches the branch lines inside the house: a valve that is not fully open, a regulator that has drifted, a leak drawing water away underground, or a service line whose opening has narrowed with rust and scale.
Narrow down the cause
Start with the simplest checks.
- Check the house shutoff.Make sure it is fully open. A valve left partly closed after earlier work is a common culprit.
- Ask about the neighborhood.If neighbors notice low pressure too, the cause may be on the utility side. Contact the City of Fullerton's water utility.
- Run the meter test.With everything off, a moving meter suggests a leak that could be drawing pressure down.
- Compare hot and cold.If only hot water is weak, look at the water heater rather than the main line.
- Have pressure measured.A plumber can gauge pressure at an outside hose bib and inside, to see where it drops.
- Inspect the regulator and line.If pressure is low right where the line enters, the regulator or the service line itself is the likely restriction.
Possible causes and clues
| Cause | Clue | Typical next step |
|---|---|---|
| Partly closed shutoff | Pressure dropped after recent plumbing work | Open the valve fully; replace it if it will not open |
| Failing pressure regulator | Pressure is low or erratic but steady at the street | Have the regulator tested or replaced |
| Service line leak | Meter moves with all fixtures off | Locate and repair the leak |
| Narrowed galvanized line | Old gray pipe, discolored water, slow decline over years | Price a service line replacement |
| Utility-side issue | Neighbors affected too | Report to the city's water utility |
Example: pressure fading for years
Illustrative example. Not a real job or customer.
A homeowner in an older Fullerton house notices showers getting weaker over several years, and the first water in the morning is slightly brown. Neighbors have no complaints.
- Confirms the house shutoff is fully open
- Runs the meter test: the meter does not move
- Sees gray threaded pipe at the shutoff and a magnet sticks to it
- Has a plumber measure pressure outside and inside
This pattern often points to a narrowed galvanized line rather than a leak. The plumber's pressure readings and inspection would guide whether to replace the service line, the interior pipes, or both.
Questions to ask
- What pressure did you measure at the hose bib and inside?
- Is the restriction in the service line, the regulator or the interior pipes?
- Would a new service line alone fix the problem I notice?
- Is there a leak affecting pressure?
Common questions
Could the city be the cause of my low pressure?
Sometimes. If neighbors also notice it, or it started suddenly, contact the City of Fullerton's water utility before hiring anyone.
Will a bigger service line raise my pressure?
A properly sized new line can restore flow lost to a narrowed old one. It cannot raise pressure above what the street supplies.
Is low pressure an emergency?
Usually not on its own. A sudden total loss of pressure, or water surfacing in the yard, is more urgent and calls for shutting off the water.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.