There are so many types of plumbing pipes and fittings it boggles my mind. And I've only messed with residental. I could only imagine commercial or industrial.
There was a older gentleman at the hardware store who I referred to as a "plumbolgist" nice and helpful as could be and no plumbing problem I gave him he couldn't solve. It's unfortunate the store closed down, because he was my go to for all things plumbing.
From what I understand, PEX is the new go-to. Expands when it freezes and doesn't crack? Not sure about the fittings though, I've seen many different kinds of fittings for PEX and have never installed any of it myself.