What causes low water pressure in a house?

Monday, September 17, 2018

What most people call low water pressure is often low water flow. The pressure is adequate, but there is a constriction or obstruction limiting the flow of water. One indicator that the problem is water flow—and not water pressure—is a brief burst of water flow when a faucet is first turned on, which then slows down. Here are several situations that could cause low water flow, but the first step in figuring it out is to determine whet the lack of water flow is at a single fixture or throughout the house. 

If the issue is only at a single fixture, try these checks: 

•• Most faucets have an aerator screen behind the spout. It collects bits of sand and debris in the water that can, over time, build into a thick layer that makes the water slow down to a trickle. If the problem is at a kitchen or bathroom faucet, unscrew the metal piece at the end of the spout.

    A small screen will fall out along with it, or may need a little tugging with your finger due to corrosion. Clean out the screen and screw the assembly back in place for an immediate improvement in water flow. Washing machines also have small filter screens that can clog. They are located inside each hose connection at the back of the machine.

•• A hot or cold water shut-off valve below a sink may be partially closed or failed. Trying to turn the valve (counter-clockwise) to make sure it is completely open is a dicey proposition with an older valve, like in the photo below, because it may start leaking at the valve stem after you turn it; and, sometimes, it will continue to leak no matter what position its set at after you have moved it. So we recommend being ready for a problem, with a few towels and a bucket handy, if you decide to check the fixture shut-off valves. 

If the problem is throughout the house, try these points:

•• Does your home have a whole-house home filter? A clogged filter will gradually reduce water flow to almost nothing. The casing for these filters is often clear, so you can see how much gunk  is in it. If the interior has a green tint, like in the photo below, that means there is a fungal growth in the bits of organic debris trapped in the filter. 

    Look for the filter at the well head or near a pressure tank. For filters with an opaque casing, it’s a good idea to keep track of the date you change the filter each time and switch it out on a regular schedule.

•• Homes built in the mid-20th century that have galvanized steel water supply piping still in service get an accumulation of rust flakes behind fixture shut-off valves, caused by interior corrosion of the piping. For some reason, the corrosion often progresses faster in the hot water pipes, so hot water flow may be worse than the cold. The photo below shows a galvanized steel pipe that was cut off just behind the faucet valve for a washing machine. 

   Replacement of the galvanized pipes is the only solution this plumbing version of arteriosclerosis. Since they will begin springing leaks as the corrosion advances further, prompt action is prudent. To learn more about aging galvanized steel pipes, visit our blog Why is old galvanized steel water pipe a problem for homebuyers?

•• A main shut-off valve may be partially closed or bad, and restricting water flow to the house. There are several places where you can find a main valve to check for this problem. If you have a municipal water system, check the water meter in the ground near the street. There is also sometimes a valve in the ground near the front wall of the home, usually below a hose faucet. In some condominiums the main water shut-off is behind or above the water heater, and it may (or may not) be marked as a main water shut-off. 

   For homes served by a well, check for a valve at the well head, near any well equipment; often in the garage or in the ground near an exterior wall of the home—again, usually below a hose faucet. Mobile homes have a shut-off valve in the crawl space just behind the skirting, and the location is marked with a small lettering on the base of the exterior wall. To learn more about main water shut-off valves, read our blog How do I find the main water shut off valve for my house?

•• A pipe leak under the floor or in the ground at the pipe from the street to the house (service pipe) can also cause low water pressure. But if it is leaking enough to reduce the pressure in your home, there would likely be visible evidence of the leakage as water bubbling up above ground, puddling around the perimeter of the home, or a wet area in a concrete floor slab.

•• If you are pretty sure that your issue is really water pressure, then buy or borrow a pressure gauge with a fitting to attach to a hose faucet outside or at the washing machine faucet. Normal water pressure for a municipal system in our area is typically around 60 to 70 psi, and private wells are usually set at 40 to 50 psi. 

   Low pressure can be a system-wide problem for a municipal water system, hopefully for a brief period. It can also be caused by a malfunctioning pressure regulator (a bell-shaped device rarely seen in our area) or undersized piping. Both of these defects are best evaluated and repaired by a professional plumber; however, one indicator of undersize piping is an abrupt drop in water flow at a bathroom when more than one fixture is used at the same time.

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Here’s links to a collection of our other blog posts about PLUMBING:

How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

Why is there sand in the bottom of my toilet tank?  

What causes a gurgling sound when a bathtub or sink drains? 

Are drop-in toilet bowl cleaner tablets safe? 

What can I add to my septic tank to help it work better?

What are the code requirements for layout of drain piping under sinks? 

Why is there mold inside my toilet tank?  

What are the pros and cons of a wall-mounted toilet?

Which plumbing fixtures require water shut off valves in a home? 

How can I tell if a house is connected to a septic tank system or sewer?

Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water? 

Why is a backflow preventer required on lawn sprinkler systems? 

How can I locate my septic tank? 

Is a hot water faucet handle required to be on the left? 

Can you live in a house while the plumbing is being replaced? 

Why is the European-style bottle trap not approved by the plumbing codes in the U.S.? 

Why can't PVC be used for water pipe inside a house? 


What are the common problems to look for when the plumbing has been replaced in a house? 

What's that powdery crust on the pipe connections at the water heater? 

How can I tell what type of plumbing pipe I have? 

Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

How do I get rid of the sewer gas smell in my house?  

What are the pipes on my roof? 

Should I wrap the water heater with an insulation blanket? 

My water bill went way up last month. How do I look for a leak?

Why does the water have a rotten-egg smell in some empty houses? 

What is an "S-Trap" under my sink? Why is it a problem? 

Where is the septic tank? Are you going to inspect it? 

What does polybutylene pipe look like? Why is it a problem?

Which water pipes are an insurance problem and possibly uninsurable? 

• Does a home inspector check the plumbing under the floor slab?

• Is it alright to disconnect the washing machine drain from the septic tank and divert it to the ground in the yard?

      Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.  


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