Home Buyers: Avoid These Flood-Prone Pipes

Poly used as main water line

Using Poly as a Main Water Line

Home inspectors often encounter poly not only used in a home’s domestic water piping but also used as a main water line.
A main water line made of poly is an intense blue color and is easily distinguishable from copper or HDPE. HDPE (high-density polyethylene) is black plastic pipe installed in new homes for the main water line.

Most real estate agents are familiar with polybutylene, but not many are aware that the main water line is equally as big a problem as the home’s potable water piping. It is just a different type of problem.

If the main water line bursts, it is highly unlikely to damage drywall and wood framing. The line will probably rupture somewhere in the yard. However, if a poly main water line bursts, a massive amount of water can be deposited right next to the home’s foundation.

And water and foundations don’t mix.

If the homeowner is on vacation or doesn’t notice the ruptured water line, it can cause significant structural damage to the home. A corner of the home may sink into the ground, there may be foundation buckling, or even large foundation cracks can appear.

Any of these foundation problems can cost tens of thousands of dollars to repair.

Acetal fittings

How Poly Install Methods Changed

There were three main developments with polybutylene.

The first type of poly piping was secured with acetal — plastic — fittings and aluminum bands. Fittings are used to connect different sections of pipe together. Poly fittings are usually the same bluish-gray color as the poly piping.

When problems began to occur with polybutylene, at first it was mainly leaking at the fittings. This is when plumbers started to use copper/brass fittings with copper bands.

Manifold poly system

Well, problems kept occurring with poly pipes — even with stronger metal fittings and bands. Plumbers began installing the manifold or “home run” poly system. With the manifold system, there was one central location where pipes were fed directly to each plumbing fixture.

The system greatly reduced the number of fittings required in typical home installations. Where an average plumbing fixture would require around 20 fittings, with the manifold system, only four to five were installed. The manifold system used long rolls of flexible poly in 20- to 100-foot lengths.

Of course, this didn’t solve issues with poly, because it wasn’t just the fittings that were leaking.

We now know that chlorinated water would cause fracturing at the fittings, but also anywhere along the pipe, and it is impossible to predict where these fractures will occur.

Copper fittings

About Hidden Poly

Around when plumbers were installing the manifold poly system, builders wanted to hide the cheap look of flexible poly piping and make it appear more professional.

Flexible poly just didn’t look good being secured to a fixture; it looked flimsy. To solve this problem, plumbers started installing copper stub outs — pipe ends that connect to a plumbing fixture to the inside of the wall. To an unknowing home buyer, it would look like the whole home has copper piping.

According to AshiReporter.org, if installed well, copper stub outs can confuse buyers, real estate agents, and even home inspectors. Using copper stub outs gave a compelling reason for builders who only wanted higher-quality copper in their builds to opt for the less expensive polybutylene.


If a buyer decides to go ahead with a home with poly, they should at least budget for the eventual replacement of the water pipes.
Even if the pipes don’t leak during their homeownership, it is highly likely that the next buyer will consider the cost of replacement.

It is strongly recommended to get at least a few estimates from re-piping specialists on a whole house replacement.
If the seller agrees, check the interior of some wall cavities with a camera scope to see if there is mold or other water damage in suspicious areas.

Also, even if it looks like the main water line is copper, always check the line at the water meter in the front yard as well to verify there isn’t poly.

Arie Van Tuijl is a licensed home inspector in Virginia and Maryland and manages HomeInspectorSecrets.com, a home maintenance education website.


  1. I was unaware of this piping, thank you for the article. I’m sure when poly was first introduced everyone thought it was robust and safe. As we do now with pex. Do you have any thoughts on comparing / contrasting poly and pex? Are we potentially making the same mistakes with pex?


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