Hi, Sometimes clay can be hard as rock and will not cut with a nozzel. If that happens then cutting the concrete may be your only option. With a circular saw and a cement blade, make lots of cuts like putting a notch in
wood. Make it extra wide, break the slots. Then steppind down inside the first notch, cut the slab again and break the notch, and once more. You should have broken through by then. Don't burn up your saw, pace it out, unless you need the water right now.
Question = since the water line is near the surface, did you plan for drainage so it doesn't freeze and break?
Happy drilling