A systematic investigation of tritium activity in precipitation, surface water, springs, and groundwater of the Roswell artesian basin in New Mexico has been supplemented by hydrogeologic reconnaissance of spring systems; by various statistical correlations and spectral analysis of streamflow and water level records of observation wells; by spring discharge measurements; by stable isotope determinations (oxygen 18 and deuterium); and by numerical modeling of part of the basin. Two recharge contributions to the Principal or Carbonate Aquifer have been distinguished principally on the basis of their tritium label and aquifer response characteristics. A ‘fast’ recharge component, of relatively high tritium activity, consists of snowmelt and storm runoff and enters the groundwater system mostly as leakage from surface drainages where these cross the karstic San Andres Formation. A ‘slow’ recharge component, low in tritium, is transmitted from the western mountains through formations underlying the San Andres. Near the western basin edge, this ‘slow’ component, in the form of springs and shallow groundwater, also feeds effluent streams which, in turn, lose most of it to the San Andres aquifer where they cross karstic zones. Almost all basin waters (including deep groundwater) fall close to the meteoric line of hydrogen/oxygen isotopic composition, and this rules out a juvenile origin or appreciable bedrock interaction.