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Pseudomonas aeruginosa isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, hemaglutinins, cytotoxins and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics, human serum sensitivity and the survival of P. aeruginosa isolates in a chlorinated environment were also examined. Of the 30 isolates tested, 16 possessed the capacity to adhere to abiotic surfaces, and 28 to adhere to epithelial cells; 30 were capable of producing hemolysins, 27 produced cytotoxins, 9 hemagglutinins, and 18 were classified as serum-resistant. For the lowest concentration of chlorine (0.2 mg/l) tested, no killing of biofilm bacteria could be discerned, even after prolonged exposure to the agent. Although all the drinking water isolates were susceptible to aztreonam, cefepime, ceftazidime, ciprofloxacin, imipenem, meropenem, piperacillin-tazobactam, and polymyxin, the P. aeruginosa isolates were resistant to one or more antibiotics. The increasing prevalence of resistance in the isolates from environmental sources may have important therapeutic implications. A notable proportion of the P. aeruginosa isolates from drinking water were able to develop virulence factors, and the incidence of virulence properties was not statistically different among the three sources. A more extensive study of the virulence properties of this bacterium by toxic assays on animals should be explored. Still more interesting would be toxicity assays on immuno-deficient animals with isolates from drinking water in order to better understand the health risk these bacteria may present.