Radio waves in the VLF band (Very Low Frequency) have a low frequency and large wavelength. This type of radio waves have the ability to penetrate deep into the bedrock and so even in water. Radio waves in the VLF band are used for communication and navigation of military shipping. Radio stations are basically on every continent.
When the primary radio waves, emitted by radio stations, hits conductive formations in the bedrock, cause by induction secondary radio waves. The electrically conductive formations may be concentrations of certain ore minerals, major water-bearing fracture zones in bedrock or karst weathering in the limestone bedrock in Somalia. With the help of a special radio receiver (in this case WADI instrument with a memory of 4000 measurement registrations) can sound out the mode for an electrically conducting geological formation and thus with relatively high accuracy indicate the location of an aquifer formation.
The strongest radio stations have a primary extension of up to 90 000 kms. For measurements, selection of all transmitters must be done to choose the one with the highest strength in the actual area.