Water Pressure Too Low? Common Causes and Fixes

Scope of this guide: This page is symptom-led troubleshooting for low pressure at one fixture or throughout a home. The linked test guide explains how to measure pressure accurately.

Low water pressure is one of the most frustrating plumbing problems - showers feel weak, filling the bathtub takes forever, and the dishwasher may not wash effectively. Most causes are diagnosable and fixable. Here's how to work through them.

Step 1: Determine the Scope

Only one fixture has low pressure: Problem is localized to that fixture (clogged aerator, failing shutoff valve, or plumbing issue specific to that supply line).

Multiple fixtures on one floor have low pressure: May be a supply line issue feeding that area of the house.

All hot water has low pressure: Problem is at the water heater or the supply to it.

All fixtures throughout the house have low pressure: Whole-house issue - pressure regulator, main supply, or municipal supply.

Pressure is lower than it used to be (gradual decline): Mineral buildup in pipes or at fixtures.

Pressure is lower than neighbors' (has always been low): Possible PRV setting issue or municipal supply problem.

Cause 1: Clogged Faucet Aerator

The aerator is the small screen at the tip of the faucet spout. It can clog with mineral deposits, sediment, and debris over time - especially in areas with hard water.

How to check: Unscrew the aerator by hand (or with pliers wrapped in a cloth). Hold it up to the light and look for mineral deposits or sediment.

How to fix: Soak in white vinegar for 1-2 hours to dissolve calcium deposits. Scrub with an old toothbrush. If it's damaged or heavily corroded, replace it - aerators cost $3-$10.

This is the first thing to check on a single-fixture low pressure problem.

Cause 2: Clogged Showerhead

Showerheads accumulate mineral deposits in the spray nozzles. Low flow or uneven spray from the shower is often a clogged showerhead.

How to fix: Remove the showerhead (usually hand-tighten, may need pliers with a cloth). Soak in white vinegar overnight. Reinstall.

If the showerhead is old (10+ years) and the flow is chronically weak, replacement is usually easier and more effective than cleaning. A good showerhead costs $25-$100.

Cause 3: Partially Closed Shutoff Valve

If pressure dropped after any plumbing work or a renovation, a shutoff valve may not have been fully reopened.

How to check: Locate the main shutoff valve (usually at the water meter connection or where the main supply enters the house). Verify it's fully open (counterclockwise to open, clockwise to close). Also check any branch line shutoffs under sinks, at the water heater, and near the fixture with low pressure.

Cause 4: Pressure Regulator Needs Adjustment or Replacement

Most California homes have a pressure reducing valve (PRV) where the main supply enters the house. Normal household water pressure is 40-80 PSI. The PRV keeps it in this range.

Symptoms of a failing PRV: Pressure was normal and then dropped throughout the house without any visible cause. Or pressure has always been low and the aerators are clean.

Testing: Buy a water pressure gauge ($15 at hardware stores) and attach it to an outdoor hose bib. Normal reading should be 40-80 PSI. Below 40 consistently indicates a pressure problem.

Adjusting the PRV: The PRV has an adjustment screw with a locknut. Turning the screw clockwise typically increases pressure, counterclockwise decreases it. Adjust in small increments and recheck.

Replacing the PRV: If adjustment doesn't hold or the PRV is failing internally, replacement costs $200-$500 for a licensed plumber to replace.

Cause 5: Corroded or Partially Blocked Pipes

In homes with older galvanized steel pipes (common in California homes built before 1970), the interior of the pipes corrodes and narrows over decades. This progressively reduces flow and pressure throughout the house.

How to diagnose: Corrosion-related pressure loss affects all fixtures and typically gets progressively worse over years.

Solution: Partial or full repiping with copper or PEX. This is a significant investment ($3,000-$15,000 depending on home size and scope) but eliminates the problem permanently and improves water quality.

Cause 6: Water Heater Issues (Hot Water Only)

If only hot water pressure is low, the problem is at the water heater: - Inlet shutoff valve not fully open - Sediment buildup in the water heater (older tank units accumulate sediment) - Kinked or corroded supply lines to/from the heater

Flushing a tank water heater (opening the drain valve to clear sediment) can help with flow in older units.

When to Call a Plumber

• PRV replacement
• Repiping project
• Main shutoff valve issues
• Any diagnosis that requires opening walls

Call your water utility first if the pressure drop is sudden and affects the whole house - it may be a municipal supply issue that has nothing to do with your plumbing.

Bottom Line

Low water pressure diagnostics: start with the aerator, then check shutoff valves, then test overall pressure with a gauge. Single-fixture low pressure is almost always the aerator or shutoff valve. Whole-house low pressure points to the PRV or main supply.

Sources and editorial notes

Prices and permit requirements vary by location, property, equipment, and scope. Treat price ranges as planning estimates and confirm current requirements with the relevant authority and contractor.

• California Contractors State License Board - when a contractor license is required
• US Department of Energy - Energy Saver
• US Environmental Protection Agency - home, indoor air, and water guidance

Related guides

• How to Test Your Home's Water Pressure Yourself
• HVAC Not Cooling? 8 Common Causes and Fixes
• Dryer Takes Too Long to Dry: Vent, Power, and Appliance Causes

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