SkyDowser is a very special sensor system, carried by a drone, which is able to map the earth's first 50m of soil at high speeds, at least an order of magnitude higher than what is currently available. Due to this big improvement the cost of groundwater monitoring is reduced by an order of magnitude as well. The sensor uses classical groundwater exploration techniques, repackaged in a light-weight fashion for operation with drones. The measured signals can be used to detect groundwater levels, determine soil moisture levels and map salt-water intrusion.