Get a dowser in. People laugh, but it seems to work.
You can try it yourself with some stiff coat hanger wire bent into right angles and held in empty felt tip cases. When they cross you are over water (if in your mind you are looking for water). Then concentrate on how deep underground it is and walk away counting your steps till they cross again, and that is approx how many feet down it is.
If you don't believe it, try it, get some friends to lay out some yoghurt pots under tea towels (about 20) in various places, with only one containing water. You should be able to find it.
I didn't believe it till I tried it by the way but some major oil companies still employ dowsers to locate oil in certain parts of the world.