@Setanta,
when Herschel first claimed that oceans existed on MArs , and that Italian guy called em channels, "Canalli" in Italian, we were exposed to a belief that there was surface water on the planet from the geomorphology of the basins and sluices.We really had no hard proof.
In 2011 another scientist claimed he saw evidence of surface water from an enclosed basin. This could not be duplicated so it died too.
In this event,Theyve got some good solid evidence based on three years of satellite reflectance data by a grad student .
I think we will need to look at the chemistry of the water solution, as well as the geometry of the seepage patterns and the extent of the sink for the runoff and infiltration (Im assuming its runnoff that is ground water bound). Best way is probably seismic survey using a towed ( an rolled out and rolled up) array of dual fqce seismic phones hooked up to something like a caltrop which was first used by Romans to deploy spikes so they would always point up no matter how they landed. A seismic survey will give a fairly accurate 3D map of subsurface density and will ID the ground water table or anything that is even partially saturated (called a vadose zone).
Id love to work on this because its actually mining (for water).
Drilling would be kinda energy intensive and rigs are always breaking down , (besides, they wouldnt get past a few 10,s of feet without human intervention and possible running out of power.
Obviously drilling will have to happen sooner or later but not as a first step. Itd be a wasted effort.
Its gonna take a goodly effort to get a 30 lb hammer lifted up on a drop table to provide the seismic energy.
We had a seismic "jug" affixed to the first Viking lander but it never recorded anything and we then assumed that Mars was essentially seismically dead. That was 1978 technology. Were in a whole nother world of data collection and sensor sensitivity.
This calls for another mission.