I know this is hard to believe, but stripping some 12 ga. wire out of romex and making divining rods may work. I was digging a drain line for a scout camp a few years ago, and asked the guy there where the line was he wanted to tap into. He used divining rods. I had to laugh thinking it was just a trick. But he gave them to me and I'll be if it didn't work. I still have them in the office and take them out to try it on our water line, Works every time. As a matter of fact once I had the line dug up and located, I tried it again, several times and the rods crossed at the exact spot of the drain line. I brought the divining rods home and both my Son and Wife tried it and it didn't work for them. But it does for me for some unexplained reason. I can even walk across the room in the house and they'll cross right where the hot water lines run for the heat registers. I wouldn't have believed it if I hadn't tried it myself.
Just bend the wire in an "L" shape (stripped of all insulation) loosely grab the wires in your clenched fist with the wires pointing forward and walk. Wires will cross when you cross a water source. That is unless you don't have the gift like my Son & Wife. lol.