Normal residential water pressure sits between 40 and 60 PSI (pounds per square inch). Anything below 40 PSI usually feels weak at the tap, and anything below 30 PSI makes it hard to run two fixtures at once.
On the other end, pressure above 80 PSI is too high. The California Plumbing Code requires a pressure-reducing valve when street pressure goes over 80 PSI, which is one of the rules we covered in our guide to the Los Angeles plumbing code.
How to Test Your Water Pressure in 5 Minutes
Before guessing at the cause, measure it. A water pressure gauge costs about $10 to $15 at any hardware store.
- Turn off every faucet, appliance, and irrigation zone in the house.
- Screw the gauge onto an outdoor hose bib closest to your water meter.
- Open the hose bib fully and read the number.
- Repeat the test at a different time of day, such as early morning and early evening.
If the reading is low everywhere, the problem is likely at the supply, the main valve, or the pressure regulator. If the gauge reads fine outdoors but one shower or sink is weak, the issue is local to that fixture or its branch line.
Why Is My Water Pressure Low? 10 Common Causes
1. Clogged Aerators and Shower Heads
If only one faucet or shower is weak, start here. Mineral deposits collect in faucet aerators and shower head nozzles and slowly choke the flow.
How to fix it: Unscrew the aerator or shower head, soak it in white vinegar for 1 to 2 hours, scrub it with an old toothbrush, and reinstall it. This one step solves most cases of low water pressure in a shower or kitchen sink.
2. Hard Water Scale Inside Pipes
Los Angeles water is considered hard, which means it carries high levels of calcium and magnesium. Over years, those minerals build up inside pipes, valves, and fixtures and narrow the path water can travel through.
How to fix it: Cleaning fixtures helps in the short term, but the long-term fix is treating the water before it enters your plumbing. Our team handles water softener installation in Los Angeles for homeowners who are tired of fighting scale. If you prefer to do it yourself, follow our step-by-step guide on how to install a water softener.
3. A Partially Closed Main Shut-Off Valve
If your water pressure dropped right after plumbing work, a home repair, or a city service call, the main shut-off valve may not be fully open. Even a quarter turn closed can noticeably reduce flow.
How to fix it: Find your main valve, usually where the water line enters the house or near the front hose bib. Turn a wheel-style valve counterclockwise until it stops. For a lever-style ball valve, the handle should run parallel to the pipe.
4. A Failing Pressure-Reducing Valve (PRV)
Many Los Angeles homes have a bell-shaped pressure-reducing valve near the main line. A PRV typically lasts 10 to 15 years. When it wears out, it can suddenly drop pressure throughout the entire house.
How to fix it: You can try adjusting the screw on top of the PRV a quarter turn clockwise to raise pressure. If that does nothing, the valve likely needs replacement. This is a job we recommend leaving to a licensed plumber because it requires shutting off the main and working on pressurized lines.
5. Old Galvanized Steel Pipes
Many homes built in LA before the 1960s still have galvanized steel pipes. These pipes corrode from the inside out, and rust buildup can shrink a 3/4-inch pipe down to a pencil-sized opening.
Signs of galvanized pipes: brown or rusty water after the tap sits unused, gray metal pipes with threaded fittings, and pressure that has gotten slowly worse over many years.
How to fix it: Corroded galvanized pipes cannot be cleaned out. The permanent solution is repiping, most often with PEX or copper. Read our breakdown of what PEX plumbing is to understand why it has become a popular choice for whole-home repiping.
6. A Hidden Water Leak
A leak diverts water away from your fixtures before it ever reaches them. If you notice low water pressure along with a higher water bill, damp spots, or the sound of running water when everything is off, you may have a leak.
How to check: Turn off all water in the house and look at your water meter. If the leak indicator dial is still spinning, water is escaping somewhere. In homes built on concrete foundations, which are very common in Southern California, the leak may be under the floor. Our guide on how to detect a water leak under a slab walks you through the warning signs.
7. Water Heater Problems (Low Hot Water Pressure Only)
If your hot water pressure is low but cold is fine, the problem is almost always on the hot side of the system. Sediment buildup inside the tank, a partially closed shut-off valve on the water heater, or a clogged dip tube can all restrict hot water flow.
How to fix it: Make sure the cold-water inlet valve on top of the water heater is fully open. Then flush the tank to clear sediment. Tankless owners should descale the heat exchanger once a year, which we explain in our guide on how to clean a tankless water heater. If the issue continues, schedule water heater repair in Los Angeles so a technician can inspect the tank and fittings.
8. A Clogged Water Filter or Softener Bypass
Whole-house filters and under-sink filters trap sediment, and that is exactly what makes them clog. A filter that has not been changed on schedule can cut pressure dramatically.
How to fix it: Replace the cartridge according to the manufacturer’s schedule, usually every 3 to 6 months. If you recently added a filter and pressure dropped, check that it was sized correctly. Our walkthrough on how to install an under-sink water filtration system covers the correct setup.
9. Faulty Fixtures or Cartridges
Single-handle faucets and shower valves use cartridges that wear out or clog with debris. When a cartridge fails, you may get weak flow at only that fixture, even after cleaning the aerator.
How to fix it: Shut off the water to the fixture, remove the handle, pull the cartridge, and replace it with an exact match. If you are replacing the whole fixture, our guide on how to install plumbing fixtures covers the process step by step.
10. Municipal Supply Issues
Sometimes the problem is not in your house at all. Water main breaks, nearby construction, and high neighborhood demand during hot summer evenings can all reduce the pressure coming from the street.
How to check: Ask your neighbors whether their pressure is also low, and check your water utility’s website for service alerts. If the whole street is affected, the utility will need to resolve it.
Water Pressure Low in House Suddenly? Check These First
A sudden drop is different from pressure that fades over years. If your water pressure dropped overnight, run through this quick checklist:
- Is the main shut-off valve fully open?
- Did any recent work happen on your plumbing or at the street?
- Is the water meter spinning with everything turned off?
- Are neighbors reporting the same issue?
- Is the pressure-reducing valve older than 10 years?
A sudden drop paired with wet walls, warm spots on the floor, or a spinning meter points to a burst or leaking pipe. In that case, shut off the main water valve and call for emergency plumbing service in Los Angeles right away.
Low Water Pressure in One Fixture vs. the Whole House
Knowing where the problem shows up narrows the cause quickly.
| Where pressure is low | Most likely causes | First step |
| One faucet or shower | Clogged aerator, worn cartridge | Clean or replace aerator |
| Hot water only | Water heater sediment, closed valve | Flush tank, open inlet valve |
| Whole house | PRV, main valve, leak, city supply | Test PSI at hose bib |
| Gets worse every year | Galvanized pipes, hard water scale | Pipe inspection |
How to Fix Low Water Pressure in House: DIY vs. Professional
Some fixes are perfect weekend projects. Others carry real risk of leaks or water damage if done incorrectly.
Safe DIY fixes:
- Cleaning aerators and shower heads
- Opening the main shut-off valve fully
- Replacing water filter cartridges
- Flushing a tank water heater
- Checking the water meter for leaks
Call a licensed plumber for:
- Replacing a pressure-reducing valve
- Locating and repairing hidden or slab leaks
- Repiping galvanized or corroded lines
- Installing a booster pump
- Any work that requires opening walls or floors
If you are wondering what these repairs might cost, our plumber cost guide for Los Angeles breaks down typical prices for common jobs.
Can a Booster Pump Help?
If your home sits at the top of a hill or at the end of a long supply line, the street pressure may simply be too low. This is common in hillside neighborhoods across Los Angeles. A water pressure booster pump installs on the main line and raises pressure for the whole house.
A booster pump only makes sense after other causes are ruled out. Adding pressure to a system with a leak or corroded pipes can make those problems worse.
How to Prevent Low Water Pressure
A few habits keep your water pressure strong for years:
- Clean faucet aerators and shower heads every 6 months.
- Flush your water heater once a year.
- Replace water filter cartridges on schedule.
- Treat hard water with a softener to slow mineral buildup.
- Have your PRV checked once it reaches 10 years old.
- Watch your water bill for unexplained increases that might signal a leak.
Frequently Asked Questions
Why is my water pressure low in only one bathroom? When only one bathroom is affected, the cause is usually local. Check the aerator, shower head, and fixture cartridge first. If both the sink and shower in that bathroom are weak, a branch line may be clogged or corroded.
Can low water pressure damage my plumbing? Low pressure itself rarely damages pipes, but the causes behind it can. Leaks, corrosion, and failing valves all get worse over time if ignored.
Why is my hot water pressure low but cold is fine? The problem is almost always the water heater. Sediment buildup, a partially closed valve, or a failing dip tube restricts hot water flow while the cold side stays normal.
Will a new shower head fix low water pressure? A shower head designed for low water pressure can improve how the spray feels, but it will not fix a leak, a bad PRV, or corroded pipes. Treat it as a comfort upgrade, not a repair.
How much does it cost to fix low water pressure? Costs range from nothing for cleaning an aerator to several thousand dollars for whole-home repiping. The only way to know is to find the root cause first.
Get Your Water Pressure Back With Hi Tech Plumbing
Low water pressure in your house is usually a symptom of something else, whether that is a clogged aerator, hard water scale, a worn regulator, or a hidden leak. Start with the simple checks above. If the pressure is still weak, or you suspect a leak or failing pipes, it is time to bring in a professional.
Hi Tech Plumbing Services Inc helps homeowners across Los Angeles diagnose and fix water pressure problems the right way the first time. Contact our team to schedule an inspection, and we will find the real cause before recommending any repair.