Human adenoviruses have been shown to occur in substantial numbers in raw water sources and treated drinking-water supplies. In one study, the incidence of human adenoviruses in such waters was exceeded only by the group of enteroviruses among viruses detectable by PCR-based techniques. In view of their prevalence as an enteric pathogen and detection in water, contaminated drinking-water represents a likely but unconfi rmed source of human adenovirus infections. Human adenoviruses are also considered important because they are exceptionally resistant to some water treatment and disinfection processes, notably ultraviolet (UV) light irradiation. Human adenoviruses have been detected in drinking-water supplies that met accepted specifi cations for treatment, disinfection and conventional indicator organisms. Within a water safety plan, control measures to reduce potential risk from human adenoviruses should focus on prevention of source water contamination by human waste, followed by adequate treatment and disinfection. The effectiveness of treatment processes used to remove human adenoviruses will require validation. Drinking-water supplies should also be protected from contamination during distribution. Because of the high resistance of the viruses to disinfection, E. coli (or, alternatively, thermotolerant coliforms) is not a reliable indicator of the presence/absence of human adenoviruses in drinking-water supplies.