Why Is There a Leaking Water Pipe Inside Your House?

Why is there a leaking water pipe in my house?

A leaking water pipe in house plumbing usually comes from corrosion, water pressure above 60 psi, freezing, a failed fitting or seal, a nail or screw puncture, or poor installation. Each cause leaves a different sign, summarized in the table below.

This guide covers the causes behind a leak in a supply or drain pipe inside your house. For a leak on the service line before your house, see our guide on leaks on the main line before the house. For what to do right now, read what to do in the first hour of a leak.

How do you tell which indoor pipe is leaking?

Start with where the water shows and how many fixtures it affects. A leak at one fixture usually points to that fixture or its supply line, while falling pressure at every tap points to a line that feeds the whole house. This is practical triage, not a measured statistic.

Identify the pipe material first

Knowing the material narrows the cause list fast. Copper points toward water-chemistry corrosion, galvanized steel points toward rust-through, and plastic pipe (PEX, CPVC or polybutylene) points toward a fitting or installation problem.

A plumber can confirm the material from any exposed section of pipe.

Hidden leaks in walls, ceilings or under slabs

A leak inside a wall, ceiling or under a slab is hard to see directly, so watch for a growing stain, a soft spot, a musty smell, or running water sounds with every fixture off. Low pressure at every tap with rust-colored water is itself a sign of galvanized failure, according to the City of St. Paul's utility guidance.

Why do copper pipes develop pinhole leaks?

Pinholes form when corrosion eats through the copper wall from the inside, and water chemistry drives much of that corrosion. Highly acidic water can leach copper from inside the pipe, leaving blue-green stains on fixtures, according to InspectApedia's review of acidic and corrosive water.

What water chemistry does to copper

Whether water corrodes or scales a pipe depends on the rocks and sediment the groundwater has touched, according to the UGA Cooperative Extension guide on corrosive or scaling water. Corrosion causes both pinhole leaks and stress cracking in copper, per InspectApedia.

How to test your water

A lab test of pH, hardness, alkalinity, total dissolved solids and temperature feeds the Saturation Index that UGA Extension describes for predicting corrosion or scaling. Ask a plumber or your water utility how to get this test done locally.

Signs of a pinhole leak

A single damaged section can often be repaired without replacing the whole line, but a water test helps a plumber decide between a patch and a longer-term fix.

Does galvanized steel pipe leak, and why does it fail?

Yes, galvanized steel pipe does leak over time. It slowly loses its zinc coating, corrodes from the inside, narrows, and eventually rusts through, according to the City of St. Paul's plumbing information for homeowners.

Low pressure and rust-colored water usually show up before the pipe fully fails.

Signs galvanized pipe is failing

• Low water pressure at multiple taps
• Rust-colored or dirty water
• Visible rust on the outside of the pipe
• Leaks at joints or along the pipe body

Lifespan depends on water chemistry and the thickness of the original zinc coating, so age alone does not prove the pipe is failing. Ask a plumber to inspect an exposed section if you suspect the house has old galvanized pipe.

What replacement means

If you notice low pressure, rust or leaks, replacing galvanized pipe with copper or PEX is worth considering, according to the City of St. Paul. A plumber can tell you whether one section or the whole run needs replacing.

Can hard water or mineral scale make a pipe leak?

Mineral-rich water can scale pipes or corrode them, depending on its chemistry, so hard water is not automatically a problem. A thin mineral coating can protect metal pipe, while heavy scale can cause harm, according to the UGA Cooperative Extension guide on corrosive or scaling water.

Whether your water leans corrosive or scaling is predicted with the same Saturation Index test described above: pH, hardness, alkalinity, total dissolved solids and temperature. Scale is one cause among several here, not usually the main one, so rule out pressure, corrosion and fittings first.

Can high water pressure make an indoor pipe leak?

Yes. The Pacific Northwest National Laboratory's service water pressure guide recommends keeping house water pressure at or below 60 psi to reduce the chance of leaking faucets and ruptured pipes. Plumbing codes require a pressure reducing valve where supply pressure is above 80 psi.

Which fixtures are most at risk

Water heaters, dishwashers, refrigerator icemakers and pressure-assisted toilets are especially prone to reduced service life or leaks above that range, according to a 2010 Building Green article on pressure reducing valves. Ask a plumber to test your pressure with a gauge if you suspect it runs high.

If a reading comes back above 80 psi, ask a plumber about installing a pressure reducing valve.

Do fittings and joints leak more than the pipe itself?

Joints and fittings are a frequent leak point, and trade experts often blame poor installation and worn seals. Their views are opinion, not a measured rate, so this page does not give a percentage.

Installation errors to check

Check for a pipe with no support, a kinked line, or an over-tightened or poorly crimped fitting. "Most leaking pipes I've encountered are leaking because they were not installed properly to begin with," one plumber told Real Homes magazine.

Drain pipe seals

Leaking drain pipes are usually caused by broken seals, according to a second trade expert quoted by the same magazine. A worn seal at a drain connection is a common, fixable cause separate from the supply side.

PEX fittings are a common supply-side leak point of their own. Our guide on fitting leaks on PEX pipe covers brass fitting corrosion and crimp problems in detail.

Can freezing cause an indoor pipe to leak?

Yes, pipes in unheated spaces are at risk. Most pipes and water meters sit in basements, crawl spaces and other unheated areas, according to the NYC Department of Environmental Protection's guide to freezing pipes. A pipe that freezes can crack, so treat a frozen section carefully even before it leaks.

Where pipes freeze

Watch pipes in a closed cabinet against an outside wall, in a crawl space, in a basement, or in an uninsulated attic. Insulate the wall and open the cabinet doors on cold nights, according to NYC's Department of Environmental Protection.

Thawing safely (one step only)

Never thaw a frozen pipe or meter with an open flame. It is a fire hazard and can cause a steam explosion, per NYC DEP.

Relieve the pressure in the line by opening the faucet first, according to University of Missouri Extension, since a blowtorch or a kerosene or propane heater can heat the pipe too fast and cause it to break.

If a pipe has already frozen and burst, see our guide on what to do when a frozen pipe bursts.

Can a nail in a wall cause a leaking water pipe?

Yes. A pipe run within 1 1/4 inches of the edge of a stud, joist or rafter can be hit by a nail or screw later, sometimes years after construction. South Carolina's adopted plumbing code requires a steel shield plate in that case for pipe such as copper or PEX.

Cast iron and galvanized steel pipe are exempt from this specific rule.

This is South Carolina's adopted code, according to the South Carolina code on pipe protection from physical damage. Many local codes have a similar rule, so check your own jurisdiction's adopted building code for the exact distance and plate spec.

A pinhole that lines up exactly with a stud, joist or rafter edge, especially near a wall where trim, flooring or fixtures were recently installed, is a clue worth mentioning to your plumber. A sudden burst is a different scenario from a slow nail puncture; see our guide on a pipe that burst inside a wall for that case.

Does polybutylene pipe leak on its own?

This page does not list specific polybutylene failure causes, because the available sources were not strong enough to confirm them. If you think your house has polybutylene (PB) pipe, a grey or off-white plastic pipe installed in some homes in past decades, have a licensed plumber confirm the material and advise on repair or replacement.

Can a shifting foundation or ground movement break an indoor pipe?

It may. Ground or foundation movement can strain a pipe's joints and connections, but this page has no sourced rate for how often that happens, so rule out corrosion, pressure, freezing and fittings first.

If you notice new cracks in walls or floors along with a leak, mention both to the plumber you call, since the two problems can be related.

Does insurance cover a leak from wear and tear?

Coverage depends on your policy and the cause of the leak, so check your own policy wording before you assume either way. Insurers often treat a sudden, accidental loss differently from gradual wear and tear.

Our guide on how homeowners insurance treats burst pipes explains how that sudden-versus-gradual distinction usually works. This is general information, not legal or insurance advice, so check your own policy and ask your insurer directly about your situation.