PE tubing is the most frequently used water line material for potable water line underground applications. Water companies and many well water systems use it extensively.
It commonally comes in ratings of 75, 100, 125, 160 and 200 psi. I suggest 160 psi. Those hose clamps are (usually) marine grade SS, not common auto hose clamps but, they rarely fail if installed correctly. Correctly being torqued correctly and not over tightened by tightening until you can't turn the screw/bolt anymore.
PE tubing is commonally sold in rolls of 100, 200, 300, 400 and 500' at most plumbing and/or pump supply houses and some big box stores. It uses insert/barbed fittings of many types and various materials. You can get tees, els, couplers, reducing couplers, female and male adapters etc.. Materails are Nylon, sch 40 and 80 PVC, brass, lead free brass, red brass, galvanized (but all galvanized should be outlawed IMO) and SS. Underground use SS or lead free brass and then use two opposed hose clamps per fitting. Opposed means one in each direction and the screw/bolt 180 degs from the other. Above ground I'd use sch 80 PVC fittings.
Unroll/straighten out the tubing in the sun for a few minutes and then wander the tubing from side to side in the trench so you don't have expansion and/or contraction problems. No sharp edges under or over it when backfilling.
Gary
Quality Water Associates