I couldn't find exactly a direct answer; what should be used for an outside, buried water line? I've seen mention of using PEX, but had the black polyethylene pipe recommended.

I'm curious because I need to put in two 60 ft runs of pipe. I'll have to either buy two 100 ft rolls of PE or a 300 ft roll of PEX for roughly the same price and then cut what I need with spare.

From what I see, they are both 160 PSI and can both be used outside, so is there any reason of one over the other?

1 Answer 1


"Black polyethylene" seems to commonly refer to HDPE pipe, which is pretty comparable to PEX. "Just" PE pipe is cheaper and less durable than HDPE - I'd advise against that underground.

PEXa ("Uponor/Wirsbo", "ProPEX", "F1960") is the best option, especially underground and in places with a potential for freezing, since it simply expands and contracts instead of bursting and leaking. However, PEXa is a bit more expensive but the advantage is it's a lot easier to route in tight areas because it's more flexible. Additionally you have the option of using "expansion" style fittings (which can't be used with other PEX types), which while they are most reliable and free-flowing of all PEX connections, typically require more expensive tools that may not be worth it for a one time job if you can't rent them. PEXa.

PEXb is the more common and typically cheapest form; connections are commonly "crimp" or "clamp" style which are more restrictive than expansion style, but the tool tends to be cheaper. (You can use those types of connections with PEXa as well.) PEXb will also expand and contract, but to a far lesser degree before risk of splitting. PEXc is also available but is rare.

A downside to PEXa vs PEXb is that PEXa leeches far more chemicals than PEXb. Aside from the health worry, the chemicals taste bad. This doesn't matter for bathrooms, but you may want to use PEXb to the kitchen, or have a dedicated drinking water spout.

Ultimately, PEX is the best option these days, but the type of PEX is more dependent on your situation.

  • If you plan to do more plumbing in the future and/or the pipe could be subject to freezing, PEXa along with Milwaukee's expansion tool (Milwaukee #2432) is the way to go for worry-free connections. There are also hand tools available for about half the price of a used Milwaukee kit ($160-200 on eBay at the time of writing).
  • If you can't rent or find the expansion tool for a reasonable price, or are simply more budget minded, PEXb using crimp or clamp style connections is likely the best path. Home Depot near me rents the tool for $16/day.
  • I used PexC for my new house plumbing supply and heating system. I am quite happy with it two years in. I also used it to run a cold line to my outbuilding. I didn't bury it very deep so I blow it out every fall with an air compressor to prevent freezing. Very inexpensive system and you can make wet changes very easily. Can't do that with copper or PVC.
    – ArchonOSX
    Commented Aug 31, 2017 at 19:59
  • 2
    To tack onto this comment a few years later, there are cheaper tools from major manufacturers like Dewalt. I did a cost comparison of HDPE and PEXa/ProPex, and by the time all the tools were sorted out it was cheaper to run PEXa in addition to being substantially more reliable and easier.
    – Eric
    Commented May 5, 2021 at 17:35
  • That's a good point about the chemicals in pexA. I had never thought of it but it makes sense that more plastisizer chemicals are required to make a more flexible pipe. Commented Jan 2, 2023 at 22:21

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