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
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.
Read more
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