"Here's how to build a low cost groundwater detection system"

Have you folks found groundwater yet at the Lab? This might help.

http://space.io9.com/heres-how-to-build-a-low-cost-groundwater-detection-sys-1656620195/+katharinetrendacosta

Resistivity testing is a tried and true method for helping to find groundwater, but this device will not reliably locate water more than a meter or two down unfortunately. And even if you had higher powered unit with enough sensitivity to get readings at more than 20+ feet, it actually takes quite a bit of training to interpret the results as the data can be effected by various factors which, if not accounted for, would give you a lot of false positives.