How to Repair Bad Water Pressure Due to Clogged Water Pipes

  • CLOGGED SUPPLY PIPES, REPAIR - CONTENTS: How to Diagnose Bad Water Pressure due to clogged water supply piping in a building. What does it mean if cold water pressure is good but hot water pressure is bad? Bad water pressure repair alternatives, which method to use; Where to replace clogged building piping to improve water pressure
  • POST a QUESTION or READ FAQs about how to de-clog or de-scale building water piping

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Repair methods for 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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Guide to Repair of Clogged Water Supply Piping and Poor Water Pressure & Flow

Clogging pipe illustrationWater pressure falls off very quickly:

[Click to enlarge any image]

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.

How to Correct Poor Water Pressure & Flow at One or More Plumbing Fixtures When Some Fixtures Flow Well

How to Diagnose & Fix Individual Clogged Faucet Strainers or Valves

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.

Slow water at the sink - check for debris or mineral clogging of the sink faucet strainer

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.

Slow water fill at a toilet - check or replace the toilet tank fill valve

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.

Slow water flow at a shower - check for debris or mineral clogging in the shower head or flow restrictor

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.

Procedure for Fixing Clogged Faucet Strainers or Valves

  • Check for clogging at the fixture faucet strainer - unscrew and clean the strainer, or if the strainer is badly corroded, bring it along to your hardware store and buy a replacement faucet strainer - they are not expensive, but sizes and threads vary a lot so be sure to buy one that fits.
  • Check for clogging inside the faucet valve itself - this will require turning off water to the fixture, disassembling the3 valve (usually possible without removing the valve from the fixture), and then slowly turning water back on to flush out debris that may have been accumulating at the valve seat.
  • Check for clogging at the stop valves (local shutoff valves) at the fixture using the same procedure.

Clogged Building Water Piping

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

How to Improve Hot 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.

How to Fix Bad Water Pressure Throughout a Building or in Large Areas:

Repairs when ALL Hot Water, all Cold, Water Fixtures, or all Both Hot and Cold Fixtures have Bad Water Pressure & Flow

How to diagnose bad water pressure in the whole building or in large areas

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

How to diagnose Bad water pressure in just some areas

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.

Clogged water pipe diagnosis & repair guides

What to Do to Improve Water Pressure Where Long Sections of Piping are Clogged or Too-Small in Diameter

sketch of water pipe diameter effectsClarification: 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.

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 abve left, the formula for area of a circle should read 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.

  • Install a water softener but remember that clogged water supply piping that has not been repaired using an acid-flush will need to be replaced. Installing a water softener won't "un-clog" mineral-clogged water pipes.

    See WATER SOFTENERS & CONDITIONERS to discuss problems with water hardness.
Improving water flow by larger pipes (C) Carson Dunlop Associates
  • Install larger diameter water piping - this method will provide piping that will deliver adequate water flow and pressure for a longer time before clogging up due to high mineral content in the water supply.

    As you can see in the sketches above and at left, Carson Dunlop Associates point out that increasing a pipe size from standard 1/2" to 3/4" in diameter more than doubles the water flow capacity in the piping! [Speaking just for me I don't understand this but I trust the engineers at CDA.- Ed.]

    Image at left provided courtesy of Carson Dunlop Associates, a Toronto home inspection and education company.

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.

When Increasing Water Flow Rate or Velocity or GPM, Watch out for Water Hammer & Water Scrubbing Damage

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 tempreature/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 llarger 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 the More Reading links shown below.

Or see PEX BRASS CONNECTOR LEAKS where we discuss corrosion build-up in brass elbows & tees that can clog PEX piping systems.

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CLOGGED SUPPLY PIPES, REPAIR at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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