Low Water Pressure in the Whole House: Common Causes
When every faucet and shower is weak at the same time, the cause is usually somewhere on the main supply, not in one fixture. Here's how to narrow it down.
Referral service: Gardena Water Line Pros is not a plumbing contractor. Your call may be connected to an independent, third-party service provider who sets its own availability, pricing and terms. Read our referral disclosure.
The short answer
Whole-house low pressure usually comes from one of five places: a main shutoff valve that isn't fully open, a failing pressure-reducing valve, old pipes narrowed by buildup, a leak in the water service line, or a problem on the utility's side. A few simple checks can tell you which one is most likely.
Step 1: Is it the whole house or one fixture?
- Only one faucet or shower is weak: the cause is usually local, such as a clogged aerator or shower head, or a worn cartridge in that fixture.
- Only the hot water is weak: the water heater or its connections are more likely than the service line.
- Everything is weak, hot and cold: keep reading. The problem is likely on the main supply.
Step 2: Ask your neighbors
If nearby homes also have low pressure, the cause may be on the public water system, such as maintenance or a break in a main. In Gardena, the water utility is Golden State Water Company. Contact Golden State Water to ask about issues in your area.
Step 3: Check the main shutoff valve
Homes have a main shutoff valve on the customer side of the meter, often near where the line enters the house or near a front hose bib. If someone recently worked on the plumbing, it may not have been reopened all the way. Only check it if it's easy and safe to reach, and don't force an old, stiff valve, because it can break.
Step 4: A failing pressure-reducing valve (PRV)
Many homes have a pressure-reducing valve (PRV) near the main line that lowers incoming street pressure to a safer level. When a PRV wears out, it can cause pressure that is too low, or too high and fluctuating. A provider can test your pressure with a gauge and tell you whether the regulator needs adjusting or replacing. Adjusting it yourself without a gauge can cause other problems.
Step 5: Old pipes narrowed by buildup
Older galvanized steel pipe can corrode from the inside, gradually narrowing the opening water flows through. Pressure drops slowly over months or years, and it's often worse when two fixtures run at once. If the service line itself is galvanized, a provider may discuss water line replacement.
Step 6: A leak in the water service line
A leak in the buried line between the meter and the house can reduce the pressure that reaches your fixtures. Other clues include wet or soggy ground, a rising water bill, and a meter that keeps moving when all water is off. Use our step-by-step water meter leak check to find out.
| What you notice | More likely cause | Who to contact |
|---|---|---|
| One fixture is weak | Aerator, shower head or fixture cartridge | Fixture repair |
| Only hot water is weak | Water heater or its connections | Water heater service |
| Neighbors have low pressure too | Utility-side issue | Golden State Water |
| Pressure dropped after plumbing work | Main valve not fully open | Check valve or call a provider |
| Pressure is low or swings up and down | Pressure-reducing valve | Plumbing provider |
| Low pressure plus wet ground or meter moving | Service line leak | Water service line repair |
What not to do
- Don't dig to look for the pipe. Gas, electric and communication lines may be buried nearby. Excavators in Southern California contact DigAlert / 811 first.
- Don't open or adjust anything inside the utility's meter box beyond reading the meter.
This guide is general information, not a diagnosis. An on-site assessment by a qualified provider is the only way to know what's happening with a specific line. Gardena Water Line Pros is a referral service, not a plumbing contractor.
Related guides
Low pressure plus signs of a leak?
Call to be connected with an independent provider who can test the line, when one is available.
Referral service: Gardena Water Line Pros is not a plumbing contractor. Your call may be connected to an independent, third-party service provider who sets its own availability, pricing and terms. Read our referral disclosure.