Underground water lines


HI. We need to replace few water lines in our mobile home park. What is the better material to use? PEX or PVC or anything else? On Lowes website I read that PEX Is not good for underground purposes. Any thoughts?


@PhillipMerrill can you suggest something?


Are they mainline pipes or service lines from the mainline to the homes? What size are they?


@PhillipMerrill those are service lines. We need to fix couple of the service lines. I believe they are 3/4"


Either pvc or pex would be fine. Im hearing a few people grumble about pex underground. The concern seems to be if it has rough surfaces it abrades over time and gets a leak. What most people miss is installation is as if not more important than the type of pipe. All pipe should have 12" of beddding under the pipe and atleast that much above or 2 times the pipe thickness on large mainline. Bedding should be sand or 3/4 minus gravel. Sand is best in my opinion


With some experience over time, I am realizing that the surface of the land moves, slowly. So where the pipes are located moves. Eventually something will give. What do you do to make sure you’re not going to have “bellies” later? Is there anything to help with lateral stress?


The ground does move over time generally the pipe moves as well. Most pipe has more “flex” in it than you would think. Concrete, clay and asbestos concrete would generally have the least the most is with HDPE (high density polyethylene, pex is a type of hdpe) the most. Joints are usually where the problems. The biggest problem areas are the settling of the fill material in the ditch itself. Sloppy excavation puts bellies or complete off sets in elevation in the bottom of the trench, no sand bedding, pipe installed over belly, throw the pipe in the ditch, throw 2 ft of dirt on pipe move on. Ditch settles joints pull apart or sewer wont flow through belly.


Multiple companies make flexible joint systems for mainline in areas with high soil movement or earth quakes see link below


Very interesting, thanks for sharing, are there locations where something like this is typical ( code say? ) When using these products, is this a high rate of failure ( as opposed to risking it with hard pipes? Or is something like this tried and true?

Would this ever be used in repairs or the application more for new installs?

Thanks for sharing, always enjoy learning new things about water and sewer from you @PhillipMerrill!


@PhillipMerrill thank you for explaining the installation. Should be 12" on the sides as well of sand or gravel?


@PhillipMerrill what is the best joint connection based on your experience? The video you shared is for bigger pipes I believe. What joint connection would you recommend for 3/4" pipe?


Pvc on 3/4 is pretty much all glue joint. Pex you have lots of options


12" sand under pipe, pipe center of ditch, 12 sand on top of pipe. Ditch width varies with trenching method. Trencher maybe 12" wide, excavator trenching bucket 12" to 18" wide


What is your opinion about Polyethylene NSF pipes?


Trade name I have called it by is just black poly. There are 3 pressure ratings (wall thickness) usually for this pipe 100 psi, 160 psi, and 200 psi.

For reference 1" schedule 40 pvc is rated to 270 psi.
2" schedule 40 is rated to 166.

Black poly is a ok product. It was pex before there was pex. Really popular in the 1970s. There are a lot of parks that are completely plumbed with black poly usually the 100 or 160 psi stuff. It was a break through product when you think of the other options in 1970 galvanized pipe where you had to cut pipe make threads, zero margin for error in install. Black poly was a mom and pop miracle peoduct in comparison. I would never use the 100, or 160 psi black poly it cracks to easy.

Black poly is simple to install just barbed fiiting and stainless hose clamp. My gripe is people buy the cheap 100 psi stuff… Home depot is selling it it must be good.

I would use pvc instead of black poly


100 psi black poly ran inside 4in black tile . 4 1inch lines per tile. Only problem after 25 years some of the 90 deg plastic barbed fittings are failing .4hr. fix not bad np failures with black poly.


@PhillipMerrill thank you for the explanation. It is clear now.

We have the black poly pipe in the park. If we do some line replacement, would you recommend to replace it with PVC? What is the connection between PVC and Black poly?


Connection is a barbed fitting on black polyside barb by pipe threads on pvc side.

How much pipe are you going to replace? If not very much i would stick with black poly. I dont like having 2 or 3 different types of pipe in one system it makes life difficult. You need spares for all three kinds of pipe, then transition fitting from one type to the other. If you have a multi year plan to replace the majority of the pipe then start with the end in mind. Go pvc but if your only talking about 5 or 10% replacement keep it all standard with the poly


@PhillipMerrill thank you for the practical advice. I need to replace less than 5%. However, I just want to develop some standard for future plumbing work. I have very clear picture now.


6% here on this one. Divide price by noi.