Causes of Varying Building Water Pressure

What are the causes of varying building water pressure?
- What causes building water pressure to change or vary over time or in cycles?
WATER PRESSURE REDUCER / REGULATOR - separate article
WATER PRESSURE REGULATOR ADJUSTMENT - separate article
WATER PRESSURE TOO HIGH: DANGERS - separate article
Questions & Answers about troubleshooting the causes of varying building water pressure
References

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This article describes the causes of variation in building water pressure for homes connected to municipal or community water supply. These different causes for variation in water pressure help tell us what is needed to improve or regulate the pressure. The process of water pressure problem diagnosis and the costs of the repair are explained.

What are the Possible Causes of Variation in Building Water Pressure?

Readers whose building is served by a private pump and well system should see WATER PUMP PRESSURE CONTROL.

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.

The water pressure regulator setting [public water supply] may not be the same as the water pressure you'll actually get in the building. Depending on the size of the building, its piping size and length of piping runs, and the number of fixtures and number of occupants (and similar variables) in a building, it is possible to draw water out of the building supply piping at such a high rate that the overall building water pressure drops considerably below the pressure setting at the water pressure regulator.

The water pressure settings on your [private water supply] well pump pressure control switch may not be the same as the water pressure you'll actually get in the building. Similarly, the private well pressure control switch settings define the maximum and minimum water pressure you may see in the system, not the water pressure you'll see at any given moment when water is being run. Even if every component of the private well, water pump, and water pressure tank and plumbing system are working normally, water pressure in such a building will fall between the time water is turned on and the time that the well pump is turned on by the pressure switch.

Number of plumbing fixtures being run at once: With a municipal water supply as well as private well water supply systems, the building water pressure seen at any individual plumbing fixture will vary depending on how many fixtures are being run. We tend to see this effect more on private well water systems where the total water supply system flow rate may be more limited.
Variation in municipal water delivery pressure: the municipal water system pressure may vary in the street as well as a function of level of water use in the whole community or when work is being done on the system.
Variation in small community water systems and private well pump water delivery pressure: with a small community well system as with private well and pump water supply, water pressure will also vary depending on the water pump on and off cycle and possibly on the ability of the well to deliver water. For example, if you turn on water at a sink just after the well pump has cut out the building water pressure will be at its "cut out" pressure maximum, typically 40 psi or 50 psi. But if water has been run in the building to drop water pressure in the system to just a bit above the water pressure control's "cut in" pressure, then the water pressure observed will be lower, perhaps just above 20 psi. Details are at PUMP PRESSURE CONTROL ADJUSTMENT.
Water pipe diameter, length, elbows and bends: Water flow rate in a building also depends on the diameter, length, and number of bends or valves in the piping system. And if water pipes become clogged with mineral deposits or debris, the water flow rate will diminish in the building, even if the static water pressure remains high. See Definition of Static Water Pressure and Definition of Dynamic Water Pressure.

Technical note: The D'Arcy-Weisbach equation for pressure and head loss can be used to calculate the actual water pressure loss due to friction in a building piping system. The Engineering Toolbox provides the D'Arcy-Weisbach formula: Δp = λ (l / d_h) (ρ v² / 2) where Δp = pressure loss (Pa, N/m²), and l = length of duct or pipe (m) and d_h = hydraulic diameter (m) and finally, ρ = density (kg/m³). But keep in mind that even this apparently accurate calculation of the effect of piping on water pressure loss will not include the effects of obstructions in building water piping such as mineral deposits, debris, or blobs of solder from an improperly-soldered copper pipe connection.
Clogged water pipes reduce water flow rate, not water pressure.
Variations in building occupancy levels: Where building demand for water flow varies widely, a single pressure reducing valve may not be able to handle the maximum water demand flow rate. This condition occurs at buildings where there is a large water supply main to an apartment or office building whose water demand can vary enormously (0.5 gpm to 100 gpm) depending on the building occupants. Watts and other pressure reducing valve producers recommend a nice solution to this problem.

As we explain at WATER PRESSURE REDUCER / REGULATOR, parallel pressure reducing valves are sometimes installed to correct this difficulty. One pressure regulator control is set at a higher psi flow rate than the other. For example installing a Watts Model 223 pressure reducer set at 50 psi in parallel with a second Watts 223 pressure reducer set to 60 psi will allow increased total water flow capacity during periods of peak water demand.
A failed hot water pressure expansion tank or significant changes in hot water temperature may also cause surges in building water pressure: some building plumbing systems include an expansion tank on the water supply system, often on the hot water piping (details about these expansion tanks are at WATER PRESSURE REDUCER / REGULATOR). If the expansion tank suffers an internal failure such as a perforated bladder, the tank will stop functioning, will not protect the system from temporary increases in hot water pressure. Also see HOT WATER PRESSURE EXPANSION RATE.
Water filter clogging: if your water system includes a cartridge-type water filter, typically installed to control or reduce sediment, debris, or odors, the filter may become clogged over time, resulting in a reduced water flow rate. Some folks confuse water flow rate (how fast water comes out of the tap) with water pressure (static pressure when water is not being run). And lots of people call our water flow rate "water pressure" which it is, in a practical sense - the pressure with which water comes out of the tap.
Variation in performance of the pressure regulator itself: a water pressure regulator may be misbehaving. One water pressure regulator failiure mode causes gradual increases in building water pressure above the set point on the regulator. This may be due to an internal failure or leak in the water pressure regulator, dirt on the regulator valve seat, or a leak in an internal regulator valveo pressure-sensing diaphraghm. See Water Pressure Regulator Testing for a discussion of regulator tests and possible repair procedures.
Variations in private water supply source, well capacity, and well pump behavior will also cause variations in water supply pressure on private well water systems. See WELL WATER PRESSURE DIAGNOSIS and WATER PUMP PRESSURE CONTROL ADJUSTMENT. Problems with the private well itself are discussed beginning at WELLS CISTERNS & SPRINGS.

How do we Diagnose Poor Municipal Water Pressure & Flow in a Building - 5 Key Checks

Key things to check when water pressure and flow are inadequate in a building served by municipal water supply are

The condition of individual plumbing fixtures, faucets, valves, and controls. A clogged sink or shower strainer will cause bad water pressure at individual fixtures while others may flow freely. A plumbing shutoff valve that is partly closed or clogged with debris will cause bad water flow at that fixture.
The incoming municipal supply pressure. The municipal water supply source may be delivering water at low pressure.
The condition of water piping between the building and the street water main. An older water supply pipe connecting the building to the water main in the street may be small in diameter, clogged with minerals, rust, or debris, or it could be leaking underground.
The condition of building water supply piping. Clogged pipes due to minerals or rust, small diameter piping, long piping

For details about the above items, see MUNICIPAL WATER PRESSURE DIAGNOSIS
The setting of the water pressure regulator at the building water meter or water shutoff valve. This topic is discussed just below.

Bad water pressure regulator or bad pressure regulator adjustment: (poor municipal water pressure) if the building is connected to a municipal water supply there may be a water pressure regulator installed, usually close to the water meter or where the water supply pipe enters the building. Photos of water pressure regulators and diagnosis and adjustment advice are at WATER PRESSURE REDUCER / REGULATOR.

If the water pressure control was set too low to start with or if there is a problem with the water pressure regulator, you may see an improvement in water pressure by diagnosing and adjusting or repairing this control.

If the loss of water pressure was sudden, it's not likely to be a problem the pressure regulator except in the less common cases of a blockage or failure in the regulator itself. In this photo our flashlight lights up a (rather amateurish looking) water pressure regulator installed on a municipal water supply.

You can see that a previous connection to the water meter was cut, left shut off (see that shutoff valve at the left hand vertical pipe - what happens if someone opens that valve?), and new fittings were installed to conduct incoming water to the building water supply piping.

The use of smaller diameter flexible copper tubing might restrict the incoming water flow, but the presence of a pressure regulator at all suggests that the incoming pressure may have been excessive. (Too high water pressure leads to fixture leaks.)

How to Adjust the Water Pressure Regulator on Municipal Water Supply

Details about how to adjust the building water pressure regulator or pressure reducing valve are found at WATER PRESSURE REGULATOR ADJUSTMENT.

We have already mentioned checking and adjusting the pressure control for the water pump on a private well system - just above. But what if the home does not have it's own well - what if the building is connected to a municipal water supply?

Watch out: don't set the water pressure reducing valve higher than necessary. Doing so wastes water and as we discuss at WATER PRESSURE TOO HIGH: DANGERS, setting water pressure too high can cause both plumbing problems and actual serious safety hazards at buildings.

A Guide to Building Water Pressure by Adjusting or Repairing the Water Pump Pressure Control Switch on a Private Pump and Well Water Supply

For details about diagnosing poor well water pressure and flow, start at WELL WATER PRESSURE DIAGNOSIS or go directly to the individual items listed just below.

How to Adjust Water Pump Pressure: The detailed, step by step procedure for inspecting and adjusting the water pressure control switch is discussed in detail at ADJUST PUMP PRESSURE CONTROL.
Diagnosing Water Pump Short Cycling on and off: If your water pump is clicking on and off too often or quite rapidly see SHORT CYCLING.
Diagnosing Water Pressure Drops without explanation when the pump stops, see Water Pressure Falls Slowly, Erratic Pumping: bad pressure control switch, building water running or leak, bad pressure gauge, bad check valve, bad foot valve.
Diagnosing & Repairing Lost Air in the Water Tank: The problem of lost air in the water pressure tank along with how to correct that condition are discussed beginning at SIGNS OF AIR LOSS.
Diagnosing & Repairing a Water Pressure Control or Water Pump Control Switch: We discuss diagnosing and repairing a water pressure control switch that sticks "on" or "off" or simply won't operate, at water pump Pressure Switch Repairs.

Frequently Asked Questions (FAQs) about the causes and cure of unexpected or unwanted variation in building water pressure

Question: Water pressure varies while taking a shower; sometimes the warm shower gets too cold

I get a noticeable water flow variation, especially during a shower. When the well pump kicks in it over powers the hot water significantly making a warm shower cold. Any ideas what I should do?

Reply: Regulating water temperature at the shower during normal pump operating cycles

If your hot water runs too cool when the water pump turns I suspect that your hot water piping or hot water source is clogged - perhaps if you are using a tankless coil that is mineral clogged this would be more likely. You could install an automatic mixing valve right at the shower - that valve is designed to keep water temperature constant; first try partly closing the individual cold water shutoff valve for your bathroom - by this I mean a valve in the cold water line that is "ahead" of or before the shower itself. By restricting the cold water flow rate in the piping you may improve the pressure balance.

But overall I suspect the problem is more likely to be clogging in the hot water piping or hot water supply system. That's because the PRESSURE produced by the pump is the same at both hot and cold water piping. It's the FLOW through piping systems that is more likely to vary. A similar effect is found when you're in the shower and someone flushes a toilet or turns on cold water at a nearby sink - and you are suddenly scalded.

If you think your hot water piping is clogged see CLOGGED SUPPLY PIPES, HOT WATER.

It is normal for building water pressure to vary between 20-40 psi or 30-50 psi depending on how your pump pressure control switch is set. Even after you've de-clogged your hot water supply you can make a still better improvement in regulating water temperature at the shower by installing an anti-scald device or valve, either at the hot water source or right in the bathroom at the fixture.

See ANTI-SCALD VALVES for details.

Question: our water pressure comes on fast but quickly drops off to nothing. Is this a clogged pipe problem?

OMG my farm house was built before christ and my pressure gauge on my well has 60 psi works fine except I don't have any pressure in the house, I can turn on a faucet and it fast then drizzles down to nothing and if the kitchen sink is running there is next to none in bathroom, if filling washing machnine there is no water upstairs untill the washer fills up. takes at least 5-7 minutes for toilet to fill and 20 for the tub. How can I get the rust out of my pipes w/o tearing the house apart. I believe that they are clogged with rust since it is hard well water. - Lisa

Reply:

Lisa if you have no actual water pressure but the gauge is reading showing pressure is present, and provided no one closed a water valve between tank and house, I suspect that the gauge pressure reading is wrong and the gauge is stuck. Try tapping on the pressure gauge to see if it moves.

The same crud that clogs the valve can clog the pressure sensing switch and interfere with proper well pump operation. If it's a rust and sediment problem your plumber might install a filter ahead of the rest of the water equipment.

Take a look at CLOGGED SUPPLY PIPING, but because the water pressure falls off quickly you'll also want to be sure that the water pressure tank is not waterlogged, causing the well pump to have to turn on and off too frequently. See WATER PUMP SHORT CYCLING to diagnose well pump short cycling and water pressure that rapidly rises and falls.

If on the other hand water pressure falls off and takes a long time to recover, I suspect that the well itself is running out of water. For that problem see How Much Water is In the Well? and also how to measure the WELL FLOW RATE.

Follow-Up:

Thank you Mr. Friedman I will certainly try that with a light touch upon looking into the well I saw a capusule looking clear plastic part rustly what is that called and maybe that needs to be replaced I posted this alittle while ago and it didn't show up I turned all water off waited opened all faucets turn back on and no water b/c all faucets were open left only kitchen and water hardly any rust or air not like it use to when we hard power failure as no lights no water. Thank you for helping me, Lisa

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Engineering toolbox properties of water - http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html editor.engineeringtoolbox@gmail.com web search 09/16/2010
"D'Arcy-Weisbach Equation for Pressure and Head Loss, used to calculate pressure or head loss due to friction in ducts, pipes, and tubes", Engineering Toolbox, web search 09/21/2010,original source
http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html
Watts, 815 Chestnut Street, North Andover, MA, USA 01845-6098, web search 09/18/2010 Watts Regulator Corporation, 815 Chestnut Street, North Andover, MA, USA 01845-6098, provides pressure and temperature relief valves, water pressure test gauges, water pressure regulators, backflow preventers, check valves, and other plumbing and heating controls and supplies. Website: http://www.watts.com/
- Watts Backflow preventers - 978-688-1811
- Watts Control valves - 713-943-0688 for example Watts pressure reducing valves, original source: http://www.watts.com/pages/learnAbout/reducingValves.asp?catId=64
- Watts Drainage products - 828-288-2179
- Watts Potable water PEX plumbing - 978-688-1811
- Watts Water safety controls - 978-688-1811
- Watts Water quality & conditioning products - 352-465-2000

Access Water Energy, PO Box 2061, Moorabbin, VIC 3189, Australia, Tel: 1300 797 758, email: sales@accesswater.com.au Moorabbin Office: Kingston Trade Centre, 100 Cochranes Rd, Moorabbin, VIC 3189
Australian supplier of: Greywater systems, Solar power to grid packages, Edwards solar systems, Vulcan compact solar systems, water & solar system pumps & controls, and a wide rage of above ground & under ground water storage tanks: concrete, steel, plastic, modular, and bladder storage tanks.
Smart Tank, Installation Instructions, Flexcon Industries, 300 Pond St., Randolph MA 02368, www.flexconind.com, Tel: 800-527-0030 - web search 07/24/2010, original source: http://www.flexconind.com/pdf/st_install.pdf [Copy on file as /water/Smart_Tank_Flexcon.pdf ] -
Typical Shallow Well One Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect_Jet_Pumps_1.pdf ] -
Typical Deep Well Two Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect.pdf ] -
Water pressure tanks - how to diagnose the need for air, how to add air, stop water pump short cycling to avoid damage - water storage water pressure tank safety.
Water pump and pressure tank repair diagnosis & cost an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
Water pressure tank failures & water pump short cycling diagnosis and repair
Water Supply & Drain Piping, water and drain pipe types, inspection, diagnosis, repairs, problem materials, clogging, etc.
Water Requirements, Home & Outdoor Living

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