The short answer
Start at the tap. If only one faucet is weak, a clogged aerator or a scaled cartridge is the likely cause. If the whole house is weak, check the main valve, the pressure regulator and the meter, then ask whether neighbors have the same problem.
Low pressure across the house usually means a partly closed valve, a failing regulator, a leak in the service line or buildup in old pipes. A pressure gauge on a hose bib gives you a number to work with, and it costs very little.
Check these in order
The easy checks come first.
- 1
Test one fixture
Unscrew the aerator and rinse it. Scale and grit often block it.
- 2
Check the main valve
A gate valve that is partly closed after plumbing work cuts flow house-wide.
- 3
Test static pressure
Screw a gauge on a hose bib with all water off. A healthy home often reads in the middle range, and a reading well below that is a problem.
- 4
Check for leaks
A moving meter with all taps off points to a leak that steals pressure. See leak detection.
- 5
Ask the neighbors
If the whole street is weak, call Padre Dam Municipal Water District.
Causes and fixes
Match the symptom to the likely cause.
| Symptom | Likely cause | Fix |
|---|---|---|
| One faucet weak | Clogged aerator or cartridge | Clean or replace, see faucet repair |
| Hot weak, cold fine | Water heater valve or sediment | Service the heater |
| Whole house weak | Regulator, valve or service line leak | Test pressure, see water service line repair |
| Pressure drops over years | Corrosion buildup in old pipes | Consider repiping |
| Pressure swings | Failing regulator or thermal expansion | Replace regulator, check expansion tank |
A gauge reading and a short visit usually settle the cause.
Pressure regulators and high pressure
Many homes have a pressure reducing valve near the main. It lowers street pressure to a safe level for the house. When it fails, pressure can drop or spike. Plumbing codes generally call for a regulator when static pressure exceeds 80 psi, because high pressure strains pipes, fixtures and appliances.
A failing regulator is a cheap part with a large effect. If your gauge reads very high, or pressure swings from low to high, ask a plumber to test and replace it. A new regulator also protects the water heater and fixtures from damage.
Hot water only
When only the hot side is weak, the heater is usually the cause. Sediment, a clogged inlet screen or a partly closed valve on the heater can choke flow. Scale from hard water makes this more common over time.
Flushing the tank and checking the valves often fixes it. If the heater is old and full of scale, replacement may be more sensible. See water heater repair for what a technician checks.
Galvanized pipes and the slow squeeze
Older homes can have galvanized steel supply pipe. As the zinc coating wears, rust and mineral deposits build on the inside, and the bore narrows year after year. Flow drops gradually, and water may turn brown after the house has been idle.
Cleaning does not fix this. Replacing the line does, and a plumber can show you the inside of a cut section so you can see the buildup yourself. See repiping for how a replacement is planned.
Testing pressure the right way
Screw a pressure gauge onto an outdoor hose bib and open the valve fully with every other water use stopped. Read the needle and note it. Then run a few fixtures and watch how far it drops.
A steady reading in a healthy range, with a small drop under load, is normal. A very low reading points to supply trouble. A very high reading points to a regulator problem. A big drop under load points to a restriction such as a partly closed valve or a corroded line.
Pressure limits in the code
The California Plumbing Code, based on the Uniform Plumbing Code (UPC), calls for a pressure regulator where static pressure exceeds 80 psi. Many homes have a regulator near the main, and it can fail in either direction, leaving pressure too high or too low.
Use a gauge on a hose bib to check. According to most manufacturer guidelines, fixtures and appliances are designed for pressure well under that limit, so a high reading is also worth fixing.
Santee note: hillsides, hard water and the district
Santee has hillside communities such as Sky Ranch on Rattlesnake Mountain, the city's highest point at 1,198 feet. Static pressure changes with elevation, so homes lower on a slope may see higher readings than homes at the top. A gauge on your own hose bib tells you where you stand.
Padre Dam Municipal Water District's 2023 report shows hardness between about 9 and 18 grains per gallon, depending on the plant. Scale clogs aerators and valves, so expect to clean them. If the weak flow is street-wide, call the district.
Sources: City of Santee history page, Padre Dam Municipal Water District, 2023 Water Quality Report.
Weak pressure in your house?
Call the 24/7 line to test and fix it.
Low pressure questions
Many homes run in the middle range, with codes generally capping static pressure at 80 psi. A gauge gives you your number.
Yes. A leak before the faucets steals pressure and flow.
Sometimes. If neighbors have it too, call Padre Dam.
It involves cutting into the main line, so a plumber is the safer choice.
Yes. See our El Cajon page for coverage.