Microbial characterization and population changes in nonpotable reclaimed water distribution systems

Changes in the microbial quality of nonpotable reclaimed water distribution systems in seven metropolitan areas of the southwestern United States were investigated by performing pathogen monitoring and bacterial growth. Water samples were collected from tertiary-treated effluents at point of entry and point of use in the distribution systems. The samples were analyzed for Cryptosporidium oocysts, Giardia cysts, enteroviruses, microbial indicators, and assimilable organic carbon (AOC). Cryptosporidium and Giardia were detected in 16% (12/77) and 43% (33/77) of nonpotable reclaimed water samples, whereas no infectious Cryptosporidium parvum were detected in any of the samples. No infectious enteroviruses were detected in any sample (0/27). At point of entry total coliform and fecal coliforms ranged from 0.7 to 280 and from 0 to 1.9 colony-forming units (cfu)/100 mL, respectively. Increases in the number of coliforms were observed as water passed through the reclaimed water distribution systems. However, no such increase in the number of coliphages was found. The chlorination practices at some utilities were not sufficient to inactivate coliforms and coliphages, but supplemental ultraviolet disinfection resulted in lower numbers of these microbial indicators. AOC levels decreased by 3-fold as water passed through the distribution systems, which inversely correlated with bacterial regrowth.