Why Is Your Main Water Pipe Leaking?

What usually causes a main water pipe to leak?

Most main leaks start with pipe that has weakened over time, or with outside forces such as shifting soil, freezing, tree roots, digging and high water pressure. Each cause leaves its own clue.

Corrosion and rust

Rust eats a metal pipe from the inside and the outside until it cracks or forms a pinhole. Eventually, galvanized pipe will rust through and leak, according to the City of St. Paul's utility guidance.

Clue: rusty or discolored water, and a leak that gets worse or better as water flow changes.

Soil movement and freeze-thaw

The soil around a buried pipe can shift as it freezes, thaws, and gets wetter or drier. That movement can stress a joint or an already weak spot in the pipe until it opens.

For freeze risk inside your home, see our guide on how to keep pipes from freezing this winter.

Tree roots

Roots grow toward moisture and find their way into small cracks or loose joints. Once inside, a growing root widens the opening it entered through.

Clue: a leak that appears near a mature tree or large shrub, or one that slowly gets worse over months.

Digging and construction

Digging for landscaping, a fence post, or other utility work can strike the line directly or disturb the soil around it. Call 811 a few business days before you dig, so your utility lines get marked first.

High water pressure

High water pressure can also stress a main line over time. The section below covers the 80 psi threshold and how to test your own pressure.

Which pipe material is most likely to fail?

Galvanized steel is the material with a confirmed rust-through failure. The other materials fail in different ways, and the material is easiest to check when the line is exposed or inspected.

Does pipe age matter?

Age is a risk factor, not a schedule. Older galvanized pipe commonly fails after decades, but age alone does not decide it.

The material, the soil, and the water conditions decide together. Check the material when the line is dug up or inspected.

How do you tell if the main water pipe is leaking or another pipe?

Read the water meter with every fixture and appliance off. If the meter keeps moving, water is leaving the system past the meter, so the leak is on the street side or in the line to your house. If it stops, the leak is inside the house or at a fixture.

How to do the meter check

Turn off every tap, appliance, sprinkler, and ice maker in the house. Note the meter reading, then check it again after a while.

Record whether the dial or the leak indicator moved. This is the common check utilities and plumbers use to tell which side of the meter a leak is on. Our guide on what a leaking water meter means covers the meter side of this test in more depth.

Can high water pressure cause a main leak?

Yes. The City of Tustin, CA says sustained pressure above 80 psi can damage on-site plumbing and may affect fixtures, and that a pressure reducing valve may be needed above that level. Test your pressure before you assume it is fine.

How to check your pressure with a gauge

1. Screw a pressure gauge onto an outdoor hose bib or a washing machine hose bib.
2. Make sure nothing else in the house is running.
3. Open the tap fully and read the gauge.
4. Compare the reading with 80 psi.

This is a simple test you can do yourself, not an official inspection.

When a pressure reducing valve is the fix

A pressure reducing valve (PRV) goes on the customer's side of the meter, and the property owner installs and maintains it, according to the City of Tustin.

Rules for exactly when a PRV is required can vary by city, so check your own city's code for anything beyond the 80 psi guidance above.

What are the warning signs before a main pipe fails?

Watch for lower water pressure, rusty or cloudy water, a jump in your water bill, a wet or soft spot over the line, a hissing or rushing sound, and any sinking ground. Any of these means check the meter and call your utility.

• Lower water pressure at your fixtures: run the meter check above before assuming it is your house plumbing.
• Rusty or cloudy water: often points to galvanized or iron pipe corroding inside the line.
• A water bill that jumps with no change in use: read the meter with everything off.
• A wet, soft, or unusually green spot over the line between the street and the meter: mark it and call your utility.
• A hissing or rushing sound near the meter box or in the yard: an underground leak is likely active.
• Sinking, cracking, or soft ground over the line: stay off that ground and call your utility right away. Our guide on how to tell if a pipe burst under your house covers more signs that show up indoors.

Who is responsible for the leaking pipe, the utility or you?

It depends on your utility. In St. Paul, the utility owns the service in the street, and the property owner owns and maintains the service on private property. Check your own utility's rules before you pay for any repair.

Some plumbing companies describe a similar split elsewhere: the owner is responsible from the meter to the house, and the county or utility usually covers the line between the meter and the main. Treat this as a general pattern, not a guarantee for your address.

Confirming which side you are on before you pay helps you avoid covering work your utility is supposed to handle, or waiting on a utility call when the repair is actually yours to arrange.

Who pays and what to do first for an outdoor break is covered in our guide on who owns an outdoor burst pipe.

Is a leaking main water pipe an emergency?

Treat it as an emergency if water is entering the house, the ground is sinking or cracking, a sinkhole has formed, or water is washing soil away. Keep people away from the sinking ground and call your utility now.

If pooling water reaches an outlet, a breaker panel, or any plugged-in appliance, stay out of that water and call an electrician or your utility before you touch anything.

For the first-hour steps, like finding and shutting off the main valve, see our guide on the first-hour steps for a leaking main.

If water has gotten into your home, drying wet areas and items within 24 to 48 hours helps prevent mold growth, according to the U.S. EPA.

Our guide on what water damage a burst pipe causes covers the drying and damage timeline in more detail.

How much does it cost to fix a leaking main water pipe?

Costs vary widely. An insurer's page cites a $1,005 national average for a main water line repair. Plumbing company estimates put a line repair at $400 to $1,500 and full main replacement at $2,000 to $5,000.

What drives the price includes how deep the pipe sits, whether the work is in the street or your yard, whether the plumber can use trenchless repair instead of a full trench, and whether concrete or paving must be cut and replaced.

Plumbers commonly cite these factors; none of them comes with a set number.

Does homeowners insurance cover a leaking main water line?

It depends on your policy and on why the pipe failed. This is general information, not legal advice, so read your policy wording and check whether it has a service-line endorsement.

• Wear and corrosion: ask your insurer whether gradual wear or corrosion on the line is a covered loss under your policy, since wording varies.
• Root damage: ask whether your policy treats root intrusion the same way as other gradual damage.
• Service-line endorsement: some insurers sell this as an add-on specifically for the underground line. Ask your agent if you have one.

Policies differ enough that you should check your own wording rather than assume either way. Our guide on does homeowners insurance cover a burst pipe covers the sudden-versus-gradual distinction insurers use.