Start by mapping the problem
- IfOnly one faucet or shower is weakThenLook at the aerator, showerhead, cartridge and that fixture's shutoff valves first.
- IfOnly the hot water is weak, everywhereThenSuspect the water heater: a partly closed valve, sediment, scale in a tankless unit or a broken dip tube.
- IfEverything is weak, hot and coldThenCheck the main shutoff, the pressure regulator and the supply line from the meter.
- IfPressure dropped suddenly across the houseThenCheck with neighbors and the city for water main work, and look for signs of a leak.
Simple checks for a single weak fixture
- Unscrew the aerator at the tip of the faucet and rinse out mineral grit
- Soak a showerhead in white vinegar to dissolve hard-water scale, per the maker's care instructions
- Confirm both angle stops under the sink are fully open
- Check whether the weak flow is only on hot, only on cold, or both
- Run the fixture with the aerator removed to see if flow improves
Whole-house low pressure in older homes
Some 1950s through 1970s Fullerton homes still have sections of galvanized steel supply pipe. Galvanized pipe corrodes on the inside, and over time the rust narrows the opening until even a fully open faucet produces a trickle. Low pressure that has slowly worsened over years, along with rusty water after the lines sit, points in this direction.
Many homes also have a pressure regulator near where the main line enters the house. Regulators can fail in either direction: stuck low, starving the house, or failing open and letting high pressure through. A pressure gauge on a hose bib tells you which you are dealing with.
Whole-house causes
| Cause | Clues | Typical fix |
|---|---|---|
| Main shutoff partly closed | Recent plumbing work or a valve that was turned | Open fully; replace if it will not open |
| Pressure regulator failing low | Gauge reading is low and the regulator is old | Adjust or replace the regulator |
| Corroded galvanized lines | Gradual decline, rusty water, older home | Replace sections or repipe |
| Leak on the supply line | Meter moves with water off, wet yard area | Locate and repair the leak |
| Supply-side work | Neighbors affected too | Check with the city |
Useful to know
- Best first tool
- A screw-on pressure gauge at a hose bib
- Hot-only problem
- Usually the water heater or its valves
- One-fixture problem
- Usually the aerator, cartridge or stop valves
- Whole-house problem
- Regulator, main valve, supply line or corroded pipe
Questions to ask a plumber
- What does a pressure gauge show at the hose bib, static and with water running?
- Do I have a pressure regulator, and is it working?
- Is there galvanized pipe in my system, and where?
- Would replacing a section fix the problem, or is repiping the better long-term answer?
Common questions
Why is pressure fine in the morning and weak in the evening?
Household demand and neighborhood demand both rise at certain times. If the drop is large, have the static and flowing pressure measured to see what your system is doing.
Can I just turn up my pressure regulator?
Some regulators are adjustable, but setting pressure too high can stress fixtures and the water heater. Have a plumber measure and set it.
Does hard water cause low pressure?
Mineral scale can clog aerators, showerheads and cartridges, and builds up in tankless heaters. It is a common cause of weak flow at individual fixtures.
General information for Golden Hills, not a quote or professional advice. In an emergency, call 911.