The Causes of Low Water Pressure

Low water pressure is a phrase often used to describe what is technically a low flow situation, where one or more fixtures in a home do not provide adequate water flow. There is a relation between pressure and flow, but it is possible to have adequate water pressure but still have low flow out of one or more fixtures. For this section, we will use “Low Water Pressure” for both low water flow and low pressure, as they both have the same effect: not enough water being supplied to the fixture.

Single Fixture Low Water Pressure

If the low pressure conditions exist only at one or just a few fixtures, we have specific recommendations that may help. For all faucets, view our Low Water Pressure in Faucets article. For showers, please see our Low Water Pressure in Shower Heads article.

Whole House Low Water Pressure

If every fixture in the house has low water pressure, the cause may be corroded piping, a restriction of the line due to a failed pressure relief valve (PRV) or backflow preventer, low municipal water flow or a valve partially closed.

Testing Water Pressure

While these can be hard to find, Pex Supply does sell hose bib water pressure gages:

These are simple to use. Make sure no water is running elsewhere in the home. Thread the pressure gage onto any hose bib, and turn on the bib. Write down the resulting pressure reading. It is your “static water pressure”.

Municipalities may supply water pressure from 20 to 100 PSI, but typical readings are 50 to 75 PSI. If your water pressure is above 40 PSI, your “low water pressure” problem is not a water pressure problem, but a problem with the flow of water through your plumbing system. If the pressure is below 20 PSI, contact your local water supplier. If you have a pressure reducing valve, or PRV, you can adjust the PRV by turning the hex head nut at the top of the bell counter-clockwise, and observing if the pressure is increased. See the PRV section below for disassembling and repairing a PRV.

Partially Closed Valves

Starting with the easiest solution first, verify that the shut off valve on the main water supply is fully open. Shut off valves are usually located where the plumbing enters the home. There are two basic types, the ball valve configuration and the gate valve configuration.

The ball valve usually has a handle similar to the image, where the long portion of the handle indicates the position of the ball diverter inside. When the handle is “in-line” with the piping, as shown in the photo, water can flow freely. Turning the handle 90 degrees shuts off the water entirely. Any position in-between restricts flow.

A gate valve, and its cousins that look similar such as globe valves, use a rotary handle to determine the position of the “gate” inside. Turning the valve handle to the right (clockwise) closes the gate, preventing water flow. Turning the valve handle to the left (counter-clockwise) opens the gate completely. Older valves may be stiff and seem frozen. Under the handle is the packing nut; using a wrench on it and turning it 1/8 turn, just barely loosening it, is often all that’s needed to “un-freeze” the handle.

Where else will valves be? If all the hot water seems to have a low flow situation, check the cold water inlet to the water heater; it should also have one of these valves. In some older homes, you may have multiple valves as plumbing has been reconfigured.

The PRV or Backflow Preventer

Pressure Reducing Valve
Some homes have a pressure reducing valve (PRV) or backflow preventer installed. A typical PRV is pictured at the right. The PRV has an internal assembly of springs and discs that regulate the pressure coming into the home. When these parts start to fail, the result can be reduced flow to the entire house.

Shut off the water before disassembling the valve. If the main water shut off to the home is before the PRV, you can use it to shut off the water. However, if the PRV is located before the main shut off, the water must be shut off at the meter or municipal supply, usually located at the edge of your property. If the parts inside the PRV are corroded or fused with mineral deposits, take all the parts to the plumbing department to obtain exact replacements. In some cases, you may have to replace the entire PRV.

Corroded Piping

Most often seen with steel or galvanized water piping after 18 to 20 years, the internal passageways of the pipe may be partially closed due to years of corrosion and mineral buildup.

Unfortunately, there is not much that can be done to correct this problem, other than replacing the pipes. This is an expensive, labor and material intensive job. There are measures you can take to mitigate the effects of it while you save to have the house re-piped.

In most cases, homes with internally corroded pipes have “full flow” fixtures as well. Installing flow restrictors in the faucets and showerheads may help, especially when multiple fixtures are being used. For faucets, modern low flow faucets with aerators will seem to provide more flow than before. This won’t help your toilet tank to fill quickly, or your washing machine to fill any faster, but it can help reduce the appearance of low flow problems for showering, washing your hands, etc.

66 Responses to The Causes of Low Water Pressure
  1. Robert
    June 8, 2013 | 4:06 pm

    I am beyond frustrated. I keep losing water pressure when 2 or more faucets are on. I had to replace my water heater which was in my crawl space. To my amazement my whole house was 1/2 CPVC so I figured I had a volume problem. So I replaced the water heater and all main lines to 3/4 CPVC. I reduced all lines to the current 1/2 going to valves. I don’t have more than 2-3 supplies on one trunk line and most of my faucets and shower valves are less than 5 yrs old from remodeling the house. All lines replaced plus the new tank and after leak test same problem. To my amazement the psi is 93 pounds at opposite ends of the house at my hose bibs. The only thing I haven’t replaced is the pressure regulator but as I said I have plenty ( actually 13 psi too much ) of pressure. I am out of ideas…..

  2. chip
    September 29, 2013 | 5:19 am

    You forgot to mention changing your homes main line filter. For those on a well this is the #1 cause of “whole house” water pressure loss. Always the 1st spot to check.

  3. Robert Bryant
    October 5, 2013 | 6:12 am

    I am on county water and not well water that’s why I didn’t mention a filter. I’ve changed everything I know to change, beyond lost on this one.

    December 11, 2013 | 3:33 pm


  5. Alisha
    January 8, 2014 | 3:06 pm

    I have been without water for 3 days we thought it was just frozen pipes for the sink in the kitchen we still had hot water and everything in the bathroom, then all of a sudden we lost all water everywhere, we replaced the pressure switch put heat by the pipes and still nothing.. Please help

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