Abstract: Process for denitrifying subterranean waters to make them potable. The sub-soil is employed as an infiltration site. Wells (3,4), for example four in number, surround a catchment well (5). The wells (3,4) are filled with a mixture based on straw and marl, to permit the denitrification reaction by a heterotrophic route by virtue of the bacteria present in the sub-soil and particularly in the subterranean waters. The denitrified water arrives at the catchment site (5) where it is withdrawn for the distribution (at 7) and for injection (8,9) into the infiltration sites (3,4). A simple, effective and inexpensive process is thus available for making potable the waters from subterranean tables.