Outdoor copper water pipe
If this is outdoors and possibly underground, understand that there are two types of hard copper pipe (as opposed to soft tubing); type L and type M. Both have the same external diameter so they both use the same fittings, but type M has thinner walls. It is for use where the pipe is going to be somewhat protected, as inside of a stud wall in a building. Type L has thicker walls so the inside diameter is slightly smaller, but it is much more resistant to accidental puncture and will last longer in terms of corrosion when in direct contact with soil. Some jurisdictions require that you use type L outdoors, so it's just better to go that way.