Hello all, and thank you fro your help.
Underground water detection is something that requires a lot of knowledge, and I don’t think there is a dedicated satellite for it.
Typically, the presence of underground water is accented by the topology, geology and geomorphology, so that the presence of water is inferred. Unfortunately, this is what I know. Perhaps somebody else will respond, but otherwise, I’d say you have quite some (literature) research to do.