The Growth and Survival of

Abstract

Ground water is an increasingly significant source of potable water that has traditionally been considered safe for human consumption without treatment. Although routinely monitored for the presence of coliforms, information concerning the non-coliform bacteria present in well water has been largely ignored. The purpose of this study was to demonstrate the ability of non-coliform, "naturally-occurring" bacteria to increase in number and persist in unamended well water. Water was collected from 19 continuously pumping wells throughout the Tucson basin and stored at in situ well water temperatures. Bacteria were enumerated using epifluorescent microscopy at predetermined intervals over a 30-day period. Greater than 3 log increases in bacterial numbers were noted after 24 hours of incubation. Maximum numbers were achieved after 3 days followed by a gradual decline ranging from 0.39-1.84 logs. Non-coliform, opportunistic pathogens have been isolated from Tucson well water. Their increase in number and survival in well water may impact the quality of untreated drinking water.