Repair methods for improving poor water pressure traced to clogs, pipe diameter, or clogged water supply piping.
This article describes How to Cure Bad Water Pressure Due to Clogged Water Supply Pipes. The process of diagnosis and the costs of the repair are explained.
What makes us think that a water pressure (really more accurately water-flow-rate) problem is due to clogged piping? A quick diagnosis that suggests that bad water pressure at a fixture or in a building is due to pipe clogging is the observation that when you first turn on the water, in that first instant, pressure is pretty good, but falls off almost immediately to a much slower level.
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When a water supply pipe pressure has been traced to supply pipe clogging there are several repair approaches that we can try. Here are some clogged piping repair attempts along with comments about how likely it is that they’ll help.
The sketch of rust clogging of galvanized steel pipe shown here, courtesy of Carson Dunlop, shows how the inner diameter of a water supply pipe is reduced by build-up inside the pipe walls. This build-up may be due to rust, mineral deposits, or other debris in the pipe.
The reduction in pipe diameter means a corresponding reduction in the flow rate seen at building plumbing fixtures. When you first turn on a faucet water pressure may be normal or "high" but as soon as water starts to flow the pressure and flow fall off to a noticeably lower level. This is the classic diagnosis of clogged water piping. But we don't know, yet, how extensive the clogging is - a single elbow, a clogged faucet strainer, or an entire length of clogged water piping can all produce this effect.
The suggestions which follow presume you’ve already followed our diagnostic suggestions to get an idea of the type of water supply flow problem that is present.
That’s important because some water pressure problems are due to water flow problems caused by a water pump, water pump pressure control, water tank, and on municipal water supply systems, flow problems may be due to problems with the water pressure regulator, water supply piping from a municipal supply, or even water meter and main water valve problems.
Watch out: people generally use the term water pressure to talk about the force or volume of water delivered at a faucet or plumbing fixture. Properly this is water flow rate; water pressure in the system is only one factor that determines the water flow rate at fixtures. Clogged pipes, partly closed valves, length of piping runs, number of ends or elbows are other factors that reduce the actual flow rate or "pressure" observed at a plumbing fixture.
Here we discuss how to correct bad water pressure due to apparent clogs in water supply piping. First we need to do some further diagnosis to determine if the poor water flow problem is at every fixture in the building or just at some of them.
Although people commonly speak of "bad water pressure" when referring to weak water flow at the tap, water flow rate is not really the same as "water pressure", though the two are related. Higher pressure will give us improved water flow rate at a fixture, but other factors such as pipe diameter, pipe length, the number of bends and elbows, and frictional loss as water runs through the system have a big effect on perceived water pressure at the tub, tap or shower.
Carson Dunlop's graph at left reviews the relationship between water pressure and water flow rate for 1/2" diameter and 3/4" diameter water supply piping. You will notice that the pressure drop when using 3/4" diameter piping is significantly less than when using 1/2" piping.
The graph also shows that for a given starting water pressure (static pressure), the water delivery pressure at any plumbing fixture will drop as the flow rate increases at that fixture. That's why the shower seems to operate at higher pressure than the tub spout: the flow rate through the small perforated openings in the shower head is usually less than through the big-mouthed tub spout.
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In discussing the difficulty of explaining pressure and flow Al comments:
It is tricky to understand that flow and pressure at a hose or faucet are inversely proportional. One of the ways I like to explain it is to think of a garden hose with no faucet attached. When you turn the tap on, the water comes out without much pressure, but it fills a bucket quickly. If you put your thumb over the hose and block most of the opening, the water comes out with much more pressure and you can spray somebody 10 feet away. However, it would take a long time to fill a bucket.
A bathtub is another good example. It takes a long time to fill a bathtub using the shower head. The tub faucet is much faster. On the other hand, the showerhead delivers a lot more pressure and is better for rinsing shampoo out of your hair. - A. Carson to D Friedman, private email, 14 May 2015
Let's also clear up the idea of what information you are getting when you measure water pressure.
Static water pressure is a pressure measurement obtained (using a pressure gauge) when no water is being run in the plumbing system. Static water pressure readings give us a starting point in understanding water pressure and flow rate in a building. In vertical pipes the water pressure is approximately 0.43 psi lower for every one foot of elevation.
We use the word dynamic water pressure for pressure readings when water is running though this simplified view gets some flack from some hydraulics engineers who have a more special use of that term.
See WATER PRESSURE MEASUREMENT if you need to measure your building's water pressure.
Carson Dunlop Associates' drawing at above- left explains that when no water is running pressure measured anywhere in the plumbing system will be the same. That's static water pressure.
In vertical pipes the water pressure is approximately 0.43 psi lower for every one foot of elevation when no water is flowing, and building height affects water pressure and flow at higher fixtures when water is flowing as well. So in tall buildings whose water supply is fed from street level or below, the starting water pressure can be quite important. Larger pipes may help improve water flow at fixtures but in buildings over three stories you may need a booster pump system as well.
See WATER PRESSURE BOOSTER PUMP.
Carson Dunlop's sketch at left illustrates a related fact that can help diagnose water pressure problems.
In sum, before looking for specific water pressure problems in the building we need to check the basics:
If poor flow is at just one fixture it’s a good bet that we can trace the flow problem to a local issue that we should be able to repair without more extensive plumbing surgery.
If the slow fixture is a sink, first check the strainer – debris-clogged strainers can simply be un-screwed. If the pressure is suddenly wonderful you need a new or cleaned strainer, that’s all.
If the slow fixture is a toilet, often the toilet tank fill valve itself becomes clogged with debris; it may be possible to remove, clean, and reinstall the valve but often it’s easier to just install a new one. We sometimes also find clogging at the small shutoff valve or water supply riser to the toilet.
If the slow fixture is a shower head, debris or mineral clogging can be diagnosed by removing the shower head and, as with the sink strainer, look for good water flow. If we find that the problem was the shower head, just replace it. Some shower head models claim to be resistant to mineral clogging by using rubber or other flexible components to form the spray.
Bad plumbing valves or bad fixture supply risers: Plumbing valves or shutoff valves to individual fixtures or valves controlling sections of water supply piping can also become clogged with debris, minerals, or even a broken faucet washer.
If you have good water pressure at all fixtures in some building areas but not any fixtures at other building areas, you may have a clog in building piping (such as due to mineral deposits, rust, or even excessive solder in new work), or mineral and debris clogged strainers at faucets and shower heads (check these first).
Watch out: especially if plumbing fixtures in different building areas are of different ages (say you added a bathroom after the building was built), bad water pressure at all fixtures in a given building area could still be due to clogs at fixture faucet strainers or valves. But if you check or clean or replace valves and water pressure is still poor in some but not all building areas, we suspect a problem with the piping serving the poor-performing areas: mineral clogs, solder or debris clogs, etc.
See WATER PIPE CLOG DIAGNOSIS - focused on clogged building water supply piping
See WATER PRESSURE LOSS DIAGNOSIS & REPAIR - addressing all causes of inadequate water pressure & flow
Poor hot water flow but good cold water flow at one or more plumbing fixtures usually diagnoses either a blockage at the water heating equipment itself or mineral clogging in the water heating system piping. Heat causes mineral precipitation out of hot flowing water faster than out of cold water, that’s why often mineral clogs appear on hot water components of a plumbing supply system first.
When only hot water supply, pressure, or flow are poor while cold water pressure is good, then we take a different approach, focusing on hot water supply equipment, piping & controls.
Note: Building water pressure that is poor at all fixtures at both hot and cold water taps may be due to clogged building cold water supply piping. Other links at the end of this article provide guides for diagnosis and repair of other causes of bad water pressure throughout a building.
Where an entire building or large building areas have bad water pressure, check to see if there is clogging at a valve, pipe section, or pipe elbow close to the water source. On occasion we’ve found that a building always had bad water pressure after a plumbing “repair” had been performed near the water tank. The installer had pushed too much solder into a pipe elbow, blocking water passage through that fitting. It was discovered by making successive cuts in the supply piping beginning back near the source to check for good water flow.
Clogged water filters cause bad water flow throughout a building and can cause water pump problems (if a private well system is installed. Water pump short cycling is discussed further
at CAUSES OF SHORT CYCLING
Where a single or one or two plumbing fittings are causing poor water pressure, due to poor installation (solder blobs), damage (broken faucet washer or other debris clogging an elbow or valve), the fix is to find and replace the culprits.
Clarification: don't confuse "water pressure" with "water flow rate". Most people think "water pressure" in the sense of how forcefully water seems to exit at a faucet or at the end of your garden hose. What you are seeing is some water flow rate in gallons per minute (gpm). If we can get a flow rate at the outlet of a faucet of 4gpm when we used to have just 2 gpm, most people call that "better water pressure" but it's really water flow rate.
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An accurate measurement of water pressure in a system is taken when no water is running, by hooking a pressure gauge up to any supply point in the system (say the end of your garden hose) and turning on the water.
For homes on a private well you probably have a (possibly reasonably accurate) pressure gauge right at the water tank. That's what we call "static water pressure" - when nothing is running, since running water somewhere will change both the pressure we measure in the system and the flow rate we'll observe when we open a second faucet.
Local piping clogs can cause bad water pressure in entire sections of hot, cold, or both hot and cold water supply pipes and fixtures in a building. Local water supply clogs due to minerals in the water may clog entire lengths of piping so badly that the only repair is replacement of the water supply pipes.
Note: the most restrictive pipe in the the water supply system determines the maximum flow rate for any water usage fixture downstream from that restriction.
[Click to enlarge any image] In case it's not clear in Carson Dunlop Associates' illustration at above left, the formula for area of a circle is Area = pi x r2
Certainly if we find that this is what’s needed, there are two approaches that can protect the investment in improved water flow. These can both be done or you may choose just one of them.
We took this second approach on a building where we found that the hot water line clogged with a combination of minerals and iron.
On cutting open the old hot water supply pipe we saw that its interior was blocked to a mere pinhole of remaining water passage. But the cold water line was basically clear. So we replaced the hot water line, including straight runs and all elbows, with a ¾” copper pipe. The repair has continued to function well for nearly 30 years.
Contact us know if you have other questions or repair ideas or if this material leaves you with a question or suggestion.
Watch out: as we discuss at WATER HAMMER NOISE DIAGNOSE & CURE, if the velocity of water in your piping system is too fast, when faucets or other controls STOP that water flow you may hear a horrible hammering or banging in the piping system. Water hammer is more than a horrible noise, it can damage equipment, cause potentially dangerous leaks at temperature/pressure relief valves, and may even cause a divorce.
A second problem with very high water velocity rates through building piping is scrubbing or wearing away of the pipe interior: a problem that occurs at very high water speeds (measured in feet per second) in piping systems. Generally the maximum safe water velocity or speed in residential water piping systems is 7 feet per second, and for 2-inch or larger pipes you should not exceed 5 feet per second. Scrubbing is more of a worry in metal piping than in the smoother (less friction) plastic piping systems. Scrubbing and corrosion are common sources of pinhole leaks in water supply piping.
Continue reading at CLOGGED SUPPLY PIPES, DIAGNOSIS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see PEX BRASS CONNECTOR LEAKS where we discuss corrosion build-up in brass elbows & tees that can clog PEX piping systems.
Or see WATER QUANTITY IMPROVEMENT - steps to increase well yield or other means to improve water flow into the well itself
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(Dec 2, 2012) Gary Los Angeles said:
Thankyou so much for your wonderful excellent helpful website reviewing and educating about these difficult plumbing problems!
Thank you so much for the nice note. We work hard to provide accurate, unbiasd information, so are of course thrilled when a reader finds our website helpful. Questions or critique help us too.
(Apr 15, 2012) Tony DAteno said:
My problem is I had good water pressure in bathroom sink, but not in shower or kicthen sink, hot and cold are fine in bathroom sink the other 2 are not. I have well water .
Tony, take a look at the bad water pressure diagnostic suggestions in
You're on the right track - if some areas have good pressure and flow and others not, I don't tend to suspect a system problem. Look for clogged strainers first, then clogged or shut valves, pipe elbows, piping.
(Apr 29, 2012) Roger Hogarth said:
I have a private well with high iron content. The water pressure fluctuates enough that my in-ground sprinklers will stop oscillating when the pressure drops and then start again when the water pressure resumes. This pressure fluctuation is also noticeable in the shower and at all faucet heads. Can you give me any ideas on what to do?
Flush out lines, acid wash piping, install an iron removal system are the rather obvious fixes that occur, but I'm unclear on why iron content or pipe clogging would cause pressure fluctuation except for one most likely cause: the pressure control switch mounting tube, water pressure sensing tube, or switch pressure sensing port is debris clogged. Try replacing those parts.
(June 12, 2012) donna chavers said:
i have calcium built up in my cold water pipes & was told to use vinegar but how do i flush it through my pipes
(Mar 17, 2014) mack lovelace said:
My sisters cold water supply is blocked. Is the anything I can do to keep from having it replaced. I have checked all the strainers, valves etc. Also replaced the jet pump and pressure tank so it must be blocked The water works fine from the faucet just past the pressure tank but not in the house. We can't really afford to have the lines replaced
a plumber can try an acid flush on your piping system - don't try it yourself as it's dangerous and also requires a pump that is not eaten up by the acid. Beware that there is a risk of pipe leaks.
Mack, from just the information in your note we can infer that the problem is not the well, pump or tank, since you have water flow past those. So you are looking for a blockage between the point where you have good water flow and the rest of the building.
If the blockage occurred suddenly I'd look for a closed or damaged shutoff valve or less likely, an obstruction at a pipe elbow or bend.
I don't assume that extensive piping replacement is necessary. More likely a series of tests beginning by examining piping between the working faucet and the next closest fixture that is not getting water, is the process to follow.
If the blockage is not total but water flow is slow at fixtures, don't forget to test by removing strainers at faucets and shower heads.
(Aug 4, 2012) Angel said:
I changed the pressure switch to the water pressure tank and now I've been with 30 persent pressure. I did replace the switch with a 30 / 50. Why no strong water pressure? help
Angel if your new pressure switch was set to on at 30 psi and off at 50 psi, and if the pump starts, runs a while, and reaches that 50 psi cutoff and stops, then your pressure tank is sitting at close to 50 psi.
But if you have poor water quantity flow at faucets (which people call poor "pressure") at one or all fixtures, pipes or fixtures or even just a faucet strainer could be clogged, as we discuss above.
Having higher water pressure doesn't help fix that problem very much since you are trying to force water through a small opening. Think of it as 50 psi through a 1-inch pipe versus 5o psi water forced through the eye of a needle. The second case is going to give you very little water flow.
(May 31, 2012) Ryan Beaudoin said:
So this might be a tough one to answer and ANY help is appreciated. At my work, in the women's restroom we have two individual stalls with 1.6gpf closets. On those we are using Sloan Royal Flushometers. About a year ago I replaced the entire sloan valve on toilet #1 because of slow flushing. After replacing the valve with no success, I replaced the toilet and smashed the old and found a piece of plastic in the trap, which could not be "snagged" by the auger.
After replacing the toilet everything went back to working as normal. Just last week we started experience the same problem. This time i pulled out the relief stem on toilet #1 and let the toilet go into a constant flush. The water drained fine and there was no buildup. Toilet #2 (which shared the same supply) when relief stem was pulled it also went into a constant flush.
Again the water drained fine, but it appeared that there was a bit more water pressure in toilet #2. Do you think I could have a partial clog in the supply line on toilet #1? Note: I replaced diaphragm on toilet one and removed the flow ring on it. It seemed to improve the flush power. Im thinking my next step would be to test the supply pressure and/or replace the toilet. Any suggestions?
Ryan, I'd think that you wouldn't have to replace the whole toilet, just pull it from its mount and inspect the entire flush route for blockage.
About water pressure, when two fixtures are quite close together and one seems to have lower pressure, while I don't rule out a water supply pipe problem (such as a big solder blob during supply line installation of the slower fixture), there can also be a problem in the flusometer itself.
(Jan 28, 2013) wayne said:
water presure good then drops fast
Wayne it sounds as if your building is on a private well & pump and that the pump is not coming on when it should AND the water pressure tank may be waterlogged.
(Mar 2, 2013) Bert said:
I had a water softener resin tank explode and dump black resin rocks into my hot and cold water lines. It plugged every "at faucet aerator" . When I remove these, there is so much resin in the line, that I have no hot water and a bit of cold at various outlets. I have bypassed the softening system (built in valves). How can I 'rinse' all this stuff from my lines?
Bert you'll need to remove all faucet strainers & shower heads to flush out the system; if that's not enough you may need to disassemble some of the water shutoff valves.
x(May 8, 2014) pink said:
my cold water tap and toilet make a shuddering noise just few months knw and none of the other units have this problem only me why can u help plse .
Pink I think you're describing a water hammer problem - please see
(June 3, 2014) Connie Jones said:
There is a water leak between the water meter leading to the house and the supply pipe immediately under the slab leading to the kitchen sink. The water meter was replaced by the city because the bottom of it had rotted. However the leak continues. When the water is turnded on from the street, the water leaks under the slab in front of the kitchen and in the yard in front of the kitchen. However it does not leak inside of the house.. What specific pieces of the water supply pipeline should be checked by a plumber? What are so possible causes of this problem?
Connie, it sounds as if the plumber will need to either excavate or drill below the slab to replace leaky supply piping or it may be less costly to abandon that supply and install new piping by another route.
(June 23, 2014) Kyle said:
Had a water main break over the winter. It was recently fully repaired. My water pressure has dropped off significantly. I have removed all strainers from faucets and cleaned out all debris. Suddenly we have very little water very little water pressure today. I suspect that there is debris in the line between the the water main and the house. What can be done to diagnose and/or repair?
Kyle, a likely clog spot could be at the house water pressure regulator.
(June 27, 2014) John said:
Water Board changed my meter outside flat, dropped card through door.. Never ever had any pressure or blocking problem before, been here years. Pressure dropped immediately, to drizzle, had to call them out. They eventually found a small piece/lump of concrete inside pipe to kitchen which caused blockage. Is it possible when an operator is changing a meter outside, for debris/pebbles/gravel etc to get in?
(July 6, 2014) how to clear water supply pipes clogged with silt said:
My well water was full of silt/clay. The water is clearing up. However, I cannot get any water from some of the faucets. I think the silt/clay is clogging the pipes. How do I clear the water pipe? Thanks Joe
Start by unscrewing the filter/strainer at each faucet, run water full-speed to flush the line; clean the strainers before reinstalling them.
We have an old tankless Instant LPG water heater. It has worked perfectly till recently. Turn on the hot water it runs fine. Turn on the cold water to mix and the temperature fluctuates from hot to cold. Cannot have a shower. Have now adjusted the hot water such that we only use the hot water and not the cold. This problem does not occur in the kitchen or the bathroom sink only the shower. The shower head is new. HELP!
Tankless heaters, most of them anyway, include a safety feature that will shut down the heater if the water flow rate through the heater is too slow - avoiding overheating and damage or unsafe conditions. When you turn on the cold water pressure you are reducing the overall house water pressure at the tankless heater inlet. That small pressure drop combined with possibly slower flow due to mineral scale deposits in the heater itself may explain the change in your tankless heater performance.
If you can find an experienced installer who knows your system it may be possible to clean or de-scale the unit, restoring its full function.
See these hot water pressure diagnosis & repair articles
(Sept 26, 2014) isa frongia said:
thankyou for all this info however after still researching on the Inspectapedia, what is the answer to the following question:
Is "acid flushing" for low water flow in a home doable on my own and how to do it?
I have this problem for all fawcets and we believe it is mineral buildup.
Please help on this one.
I don't recommend do-it-yourself acid flusing of water pipes. An experienced plumber will get the job done faster, safer, and probably at lower cost than you can because she will
(Sept 27, 2014) ARUN MISHRA said:
The water supply which we receive from muncipal corporation is very dirty due to some supply problems. We cannot even use it for domestic purposes such as bathing washing etc. Is there any method to improve the water standard by use of any external kit for the whole bulding.
Arun, I would
(Sept 30, 2014) Jenn said:
Hello! Wondering if you can help with our water problem. About a week ago we noticed that our pump was running full time and not turning off. We took the pump off the line and took it in for repair. They made a quick (and cheap - $45) repair and told us it was good to go. (We're still not sure what they fixed.) We put the pump back on and still the pump would not shut off. We finally got a pressure gage and discovered that the pressure at the pump was only 10psi. Today we pulled up the intake pipe and replaced the foot valve, hoping that would solve the problem. It's got the pressure up to 15psi, but still not enough pressure to shut the pump off. We have added air to the pressure tank, primed the pump every time we've disconnected it, put a new pump switch electrical box on the pump, and still nothing. We can turn the pump on enough to get some water in the house, but the pressure is poor, and the toilet tank won't fill....and the pump still runs.
Our well is fairly shallow (the foot valve is about 25' below ground) but we can see water in the well casing. We are at the bottom of a valley next to a river bed and we are pretty sure the water supply is not the problem, but are inclined to try a new pump, or take the old one in again. Any advice you can offer would be helpful...we're at our wits end!
the diagnostics at
should help you find and fix the trouble. Let me know if you need more help.
Oct 10, 2014) goltu jain said:
my water supply line has block by water iron so how to clean the same as our innerline fitting in building
(Oct 31, 2014) Anonymous said:
Two years ago the water district came out and changed the meter at the curb. After that I noticed my water pressure decreased. Over time, I can only use one faucet at time. I cannot take a shower with the washing machine running at the same time. The digital indicator flashes "no water" and the washing machine starts beeping. The water pressure in the entire home is extremely low. I notified the water district of the problem, and they came out to test the water pressure. Of course the pressure was fine from the street. The water district advised the problem was on the property. I have the turned the water valve as far a I can to get the most water possible. Ignoring the problem is not making it better. Any suggestions?
Possibly the repair resulted in a blockage due to improper soldering or release of debris into the water system.
Pressure and flow are NOT the same thing at all. Measuring pressure alone won't diagnose this problem and is misleading.
Measure the flow rate at a faucet closest to the incoming water main.
(Nov 11, 2014) EM said:
Have low cold water pressure at my sinks. System is residential well with water tank installed 1981 and has a gauge pressure of 30 psi and a 28 psi at the top valve? With no filter at sink hot water runs steady flow and clod is slower running?
What may be the problem? Is it the old water tank that needs replaced or another issue?
(Apr 30, 2015) Robin Layton said:
it appears as if your illustrated formula for finding area of a pipe is incorrect. although your answer is correct the formula isn't. area of a circle is pix r squared. not pi times r as you have listed. I understand this as you are plumbers after all. but misleading
Thank you so much, Robin, I'll correct the text above. I don't know how our exponent on the radius r got lost in the illustration but I've contacted Al Carson who informs me we were using an obsolete sketch. Al provided and we have inserted updated illustrations. Cason Dunlop Associates, a Toronto home inspection and education company have graciously shared technical information and illustrations with InspectApedia.com
We appreciate your careful eye and editing and more, taking the time to write.
1 June 2015 gene said:
i replaced a broken section of pipe but now i have no water pressure tho the pump is pressrized where iyt needs to b and i can hear water in the pipes at the main to the house?
I'd look for a solder or debris-blocked pipe or elbow or sink strainer screen or pressure regulator inlet, or for a valve someone forgot to open.
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