There’s nothing more frustrating than turning on the shower only to be met with a weak, barely-there trickle. Low water pressure can make everyday tasks feel like a chore, from rinsing dishes to filling a pot on the stove.

If you’ve been asking yourself, “What causes low water pressure in a house?” you’re in the right place. In this guide, Crown Plumbing explains the common causes and warning signs so you can decide when professional plumbing service in San Jose is needed.

What Is Considered Low Water Pressure?

Residential water pressure is typically 45 to 65 PSI, and anything below 40 PSI is generally considered low and can noticeably affect how water flows through your fixtures. Low pressure isn’t always a plumbing emergency, but it’s a signal that something in your system deserves attention.

Common Causes of Low Water Pressure

Knowing what causes low water pressure in a house makes it easier to narrow down the problem before calling a plumber. Here are the most frequent causes to check first:

• Water pressure regulator failure: A water pressure regulator controls the pressure entering your home from the main line. When it malfunctions, pressure can drop suddenly throughout your entire house.
• Plumbing leaks: Plumbing leaks divert water before it reaches your fixtures, resulting in weak flow at faucets and showerheads. Leaks can be visible under a sink or hidden inside walls, under floors, or buried underground.
• Mineral buildup in pipes: Hard water deposits calcium and magnesium inside your pipes over time. Mineral buildup gradually narrows the passage water flows through, causing pressure to drop slowly across your home.
• Clogged fixtures: When low pressure affects only a single faucet, sediment or mineral buildup in the aerator may restrict flow at that fixture.

If the problem is widespread rather than isolated to a single fixture, the cause is likely deeper in your system.

Pipe and Valve Problems That Gradually Reduce Your Water Pressure

Some of the most serious causes of low water pressure develop inside the pipes themselves. Corroded water pipes are a common problem in older homes, particularly those with galvanized steel plumbing. Galvanized pipes corrode from the inside out, and as buildup accumulates, the pipe’s usable diameter shrinks.

Partially closed shut-off valves are another overlooked culprit. Your home has a main shut-off valve near the water meter, plus individual valves under sinks and behind toilets. If any of these were not fully reopened after repair, the pressure on the affected fixtures will be reduced.

When the Problem Is Outside Your Home

To understand what causes low water pressure in a house, you also need to consider the water supply before it reaches your plumbing.

Municipal water supply issues affect entire neighborhoods at once. Utility repairs, main line issues, or peak demand can all cause temporary pressure drops. If your neighbors are experiencing the same problem, contact your water utility to ask about known issues.

Shared or over-split supply lines are another possible cause, particularly in homes that have been renovated or expanded. When a single supply line is divided to serve too many fixtures, water gets pulled in too many directions simultaneously.

Get Help With Low Water Pressure in San Jose

Now that you know what causes low water pressure in a house, the next step is finding where the pressure loss begins. If you are noticing signs that your home needs repiping or can’t pinpoint the source of your pressure problem, our team is ready to help.

A professional inspection can identify the source and help you choose the right repair before the problem gets worse. Call Crown Plumbing at (669) 219-2233 to schedule service in San Jose.

Frequently Asked Questions

Low water pressure can have several causes, so the following will help you understand what may be affecting your home’s plumbing system.

Can Low Water Pressure Affect Only Hot Water?

Yes, when only hot water pressure is weak, the likely cause is sediment buildup inside the water heater or a partially closed valve on the heater itself.

How Does Hard Water Lead to Low Water Pressure?

Hard water carries elevated levels of calcium and magnesium that deposit on the interior of pipes over time, gradually narrowing the passage water flows through and reducing pressure.

What Causes Low Water Pressure in a House Across Every Fixture?

When low pressure affects the entire home, the cause is usually a larger system issue, such as a faulty pressure regulator, a partially closed main shut-off valve, municipal supply problems, or aging pipes restricting flow.