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WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS
WATER CONSERVATION MEASURES
WATER CONTAMINANT LEVELS
WATER FILTERS, HOME USE
WATER HAMMER NOISE DIAGNOSE & CURE
WATER ODORS, CAUSE CURE
WATER PUMP REPAIR GUIDE
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER PUMP SHORT CYCLING
WATER SOFTENERS & CONDITIONERS
WATER TANK REPAIR PROCEDURES
WATER TANK: USES, TROUBLESHOOTING
WATER TESTS, CONTAMINANTS, TREATMENT
WATER TREATMENT EQUIPMENT CHOICES
WELLS CISTERNS & SPRINGS
WELL CHLORINATION & DISINFECTION
WELL FLOW RATE
WELL WATER PRESSURE DIAGNOSIS
WELL YIELD IMPROVEMENT
WINTERIZE A BUILDING
How to measure municipal or well water water pressure at a building: this article describes how to measure water pressure and water flow in buildings in order to diagnose bad pressure or bad water flow.
The process of water pressure problem diagnosis and the costs of the repair are explained. We explain the difference between measuring static water pressure (nothing running) and dynamic water pressure.
We explain the difference between water pressure, and water flow rate, and we describe how to measure water flow rate in a building.
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How to Measure Building Water Pressure: Definitions of Static Building Water Pressure & Dynamic Water Pressure
Distinguishing between static water pressure, dynamic water pressure, and water flow rate can help diagnose water problems in a building. Here we explain these concepts and we describe how to measure water pressure and flow at a property where either municipal water supply or a private well and pump water supply is in use.
Static water pressure is the pressure shown anywhere on the water supply piping system when no plumbing fixtures are running.
Typically on a municipal water supply the static water pressure in the building will be 30-60 psi, depending only on the setting of the water pressure regulator - the regulator determines static water pressure in the building.
On a private well and pump water supply system water pressure varies between 20-40 psi or 30-50 psi depending on the equipment installed and the pump pressure control switch settings.
Our photo (left) shows a simple and inexpensive home-made water pressure measuring gauge that we attached to the cold water faucet for a washing machine hookup. Building suppliers also sell water pressure gauges with the same fittings to attach the gauge to a hose or faucet hookup (see our page top photo).
To measure static water pressure, attach a pressure gauge anywhere in the building on water supply piping. Make sure that no plumbing fixtures are running, and if the building is served by a well and pump system, make sure that you have run water until the pump starts running, then turn water off. The pressure read on the gauge with all fixtures "off" is the maximum static water pressure at the building.
Dynamic water pressure is the pressure shown anywhere on the water supply piping system when one or more plumbing fixtures is drawing water. You can see that the more fixtures that are running, the lower the dynamic water pressure will be.
On a municipal water supply system the dynamic water pressure and flow seen in a building will drop to a number lower than the static water pressure but will normally remain steady when you turn on one or more plumbing fixtures.
On a pump and well water supply system the dynamic water pressure and flow seen in the building will drop to a lower number than the static water pressure, and will also vary as the pump cycles on and off.
Example of variation in building water pressure:
On a pump and well water supply system when multiple plumbing fixtures are operating, the dynamic water pressure will fall to a lower number and will hover there once the quantity of water being drawn causes the pump to turn on and stay on - that is, when you are running water fast enough that the pump cannot "get ahead" of the water draw out rate.
How much pressure is exerted by water per vertical foot of pipe or lift or rise?
Reader question: 3/3/2014 Rob Cunningham said: What is the water pressure per foot, I know it is 2.??? per foot but I don't remember the the formula.
Reply: basic data about water weight, volume, pressure relationships - basic hydraulics of water
The pressure of water is usually stated in psi or pounds per square inch. Here are some water volume, weight & pressure basics:
How much does a gallon of water weigh?
How to Translate the Height of a Column of Water to Pressure or PSI
The pressure exerted by a vertical column of water inside of a well casing or a pipe, measured at the bottom of that column, is determined as follows:
Do we need to convert the weight of water to pressures per foot in a well pipe or inside the well casing?
No. Using the formula given just above,
This formula is accurate regardless of the pipe, casing, or well shape or diameter. Height matters, but not diameter.
We can calculate the water pressure at the bottom of any vertical height. But for water inside of a well or well casing, we need to be sure that we are calculating correctly by counting only the height of the column of water, not the total height that for most wells (except artesian wells) will include an air space above the top of the column of water.
The size or volume of water inside of a well or well casing when the well is at rest (not in use) and has fully recovered from any recent use (the well has re-filled from its water source) is defined as the static head.
At STATIC HEAD, WELL DEFINITION we show how to calculate the volume of water in a cylinder of various diameters. Recapping:
Thanks to reader Gary A Sale for pointing out confusion in an earlier version of the text above. - 4 Dec 2014
Other water conversions weights & measures converting a U.S. gallon
Static municipal water pressure may vary at different times of the day depending on what pressure is being delivered by the municipal supplier. In some communities municipal water pressure varies little while in others the variation can be significant.
To measure municipal water pressure in a building, use a water pressure test gauge like the home made water pressure test gauge shown above or the store-bought water pressure gauge shown at page top.
Install the water pressure gauge at a convenient outside hose bibb or to the drain connection on a water heater, or at a washing machine hot or cold water hose connection point.
If the building water pressure gauge reading is below 60 psi, leave the gauge in place for two days, checking it frequently for different pressure readings, because water pressure may vary by time of day or by the plumbing fixtures in use in the building.
An advantage of the store-bought Watts water pressure test gauge over the home-made version is that the special Watts test gauge includes a high-point red indicator needle that will record the highest water pressure sensed by the gauge during the test period, even if you did not happen to be looking at the gauge when that condition occurred.
Since your water pressure measurement itself could be inaccurate,
see WATER PRESSURE GAUGE ACCURACY where we explain causes of false high water pressure readings and false low water pressure readings.
For pressure gauge repair or replacement
How to Interpret Your Municipal or City Water Pressure & Flow Measurements
If your dynamic water pressure is too low on a municipal water supply system you can boost building water pressure by installing a pressure booster pump and water tank.
Also see our discussion of parallel water pressure reducing valves found
If your municipal or city water pressure is always too low, perhaps below 30 psi,
For more help figuring out why your municipal water pressure is too weak,
then see MUNICIPAL WATER PRESSURE IMPROVEMENTS.
Also see WATER PRESSURE VARIATION CAUSES.
Watch out: If the building water pressure gauge reading is ever found at 80 psi or higher, you will want to install a water pressure regulator at the point where water supply enters the building. Watts produces a Watts Governor 80™ used for this purpose, but other manufacturers also produce a wide variety of water pressure regulators.
If your building already has a water pressure gauge installed, it may be defective or it may be set too high. If your static water pressure is too high on a municipal supply,
At HOT WATER PRESSURE EXPANSION RATE we discuss how we measure water pressure and how temperature changes affect water pressure in a closed water heater tank or heating boiler.
Static well water pressure depends on the setting of the pump controls. You can try reading the water pressure shown on the pressure gauge that is usually installed at the pressure tank or near the pump pressure control switch.
Watch out: dirt or debris in the small diameter pressure switch mounting pipe at your water pressure tank, or a failing pressure gauge itself can give inaccurate water pressure readings. Particularly if your water pressure gauge reading does not rise and fall smoothly as the water pump turns on and off, you may want to replace the gauge and/or make an independent water pressure reading using the water pressure test gauge we have described just above.
Since your water pressure measurement itself could be inaccurate,
How to Interpret Your Private Well Water Pressure & Flow Measurements
If your dynamic well water pressure is too low on a private pump and well system you may be able to boost water pressure by adjusting the pump pressure control switch.
Also, because poor water flow rate from a private well system is often due to a limitation of the well's flow rate,
Diagnosis of private water well problems divides roughly into these areas
This topic has moved to WATER FLOW RATE MEASUREMENT - live link given just below.
Watch out: measuring "flow rate" at any faucet or fixture served by a well pump system will be inaccurate and will reflect pump capacity, piping restrictions, fixture restrictions, and even actual well flow rate variations where pump protection tailpieces or similar devices are installed. Measuring flow rate at a fixture does not measure the well's true flue rate.
Continue reading at WATER PRESSURE VARIATION CAUSES or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: Does closing a water supply pipe stop valve part way reduce water pressure in the building?
this may sound silly but by reducing the flow via the stop tap do you reduce the pressure - Allan
Reply: No. But it will reduce the water flow rate. Here is the difference between water flow rate and water pressure
Does closing a stop valve reduce water pressure? Well yes if you mean flow rate and no if you mean static water pressure in the system.
Question: how does adding plumbing fixtures reduce the water flow rate & what is the difference between upstairs & downstairs water pressure?
(July 4, 2011) mike in p.s. said:
I own a condo with the following: 2-Tub/Shower Combo's, 2-Toilets, Dishwasher, Kitchen Sink, 4-Bathroom Sinks, 1-Patio Faucet. My unit is upstairs with an identical unit below (same fixture count). Each unit HAD it's own 3/4" feed with seperate shut-off vales about 30' away at the common meter box. HERE'S the problem.
The downstairs unit had a leaf in their line undeer the slab and aftere two days of attempting to locate and repair the line the plumbers deceided to abandon the downstairs fee and tee into our 3/4" feed so now both units share one feed, escentially doubling the number of fixtures on one 3/4" line.
Additionally am I correct in thinking that because I am upstairs and if both units are using water, the downstairs unit gets more pressure? And ideas would be helpful!
If your pressure upstairs is unacceptable it may be possible to improve things with a separate pressure tank and booster pump. In the article links at page left, under
Question: how do I get more water pressure?
(Oct 19, 2012) sly said:
How do you increase the water pressure in your building building, because the water flow rate is low.
Sly: you might want to install an auxiliary water pressure tank and booster pump. See WATER PRESSURE BOOSTER PUMP
Question: pressure of water per foot of height
(Mar 3, 2014) Rob Cunningham said:
What is the water pressure per foot, I know it is 2.??? per foot but I don't remember the the formula.
Here are some water weight & pressure basics:
At 30-feet of water (say diving under the ocean) at sea level, you've equaled 1 ATM of pressure.
The Weight per US gallon of water is based on 7.48 gallons per cubic foot.
1 Gallon (U.S.) = 3.785x10-3 m3 = 3.785 dm3 (liter) = 0.13368 ft3 = 4.951x10-3 yd3 = 0.8327 Imp. gal (UK)
Details of this calculation showing how to convert the weight of water to pressures per foot in pipes of various diameters or inside the well casing are given in the article above.
Question: water piping size
(Nov 14, 2011) Anonymous said:
what size of waterline from meter pit to house at 600'
Anon typical residential water piping uses 1" to 1.5" ID piping but the size that you need to use depends on several factors including required flow rate, delivery pressure, elevations, distances, and the required number of elbows or bends - so your plumber may have her own recommendations.
(Jan 4, 2012) need of water presure pump said:
I am planning to install a water misting
(July 15, 2014) SUMOD said:
Hai,in a 3/4 inch 40m lenth pipe is connected with pressure pump and it is closed at the end and the pressure is 7 bar once the valve will opened the pressure is dropping to 4 bar.how to calculate the flow rate.
12/3/2014 garyasale said:
Hello guys, I do not mean to split hairs here, or rather a few oxygen and hydrogen molecules, but if water weighs 62.4 LBS/cu.ft, and there are 7.48 gallons/cu.ft., then water must weigh 8.34 LBS/gal. not 8.25 as indicated in your article.
Also, in your example regarding pressure: I read in your article that a container 12" x 12" x 12" (a cu.ft. of water has a pressure of 62.4 pounds/sq.ft which doing the math would be .433 psi. Now we previously established that a cu.ft of water is 7.48 gallons weighing 8.34lbs. Then I read that a volume(your example was a 6" well casing containing 1.46 gallons has a pressure of .426 psi. Your explanation suggests the difference is due to the difference in weight. My understanding is that the weight is not a factor, and to illustrate this point, I suggest you put a pressure gauge at the bottom of a pipe 12" in diameter, and one at the bottom of a 1" diameter. If both are 1 foot high, they would both read .433 psi. There is .433 psi per foot elevation regardless of the size of the container and therefore regardless of the overall weight of the water. A water tank one foot high which holds 300,000 gallons of water would be have a water weight of 2.5 million pounds would have a pressure of .433 psi.
Thanks, Gary. We'll review the article text.
We've no intention to try a repeal of the basic laws of physics. One goes from a cubic foot to the volume of a cylinder to do the same calculations. What can indeed be confusing (we'll edit the article as needed) is that one linear foot of water in a 6-inch diameter x 12-inch tall well casing is not going to equal a cubic foot in total water volume. The pressure exerted by any volume of a substance is a function of its height (or depth) as you discuss.
The weight of any total volume of water above a specific number of square inches (the area of a circle at the bottom of the well casing) is calculable.
Moving to your example, let's look at scuba diving.
Let's dive down to 32 feet below sea level in sea water. Water pressure is now 2 atmospheres or 29.4 psi (little enough to be safe from getting the bends even if we hold our breath a long time or swim around using a SCUBA tank).
Container size is not a factor in the example.
Thanks for the comments. We've reviewed and edited the original text to remove some confusion.
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