For Science Hack Day 2014, our team created a low-cost groundwater detection is necessary to measure groundwater usage on a wide scale.
The following is from the presentation given at Science Hack Day.
Space electrodes evenly
Inject current in OUTER pair
Measure voltage across INNER pair
z = a / 2
ρ = 2 π a V/I
ρ low = WATER!
ρ high = DRY!
a increases, the depth of signal increases