Abstract
AbstractA prior study of 12 potable water distribution systems detectedLegionella pneumophilain only one of 576 samples (0.17%), but the survey was conducted during winter and spring months when water temperatures were generally below 15°C (LeChevallier,AWWA Water Science2019, e1122). Ten of the utilities agreed to participate in a second round of testing during the summer and early fall months when water temperatures averaged 23°C (average temperatures ranged from 14 to 29°C).L. pneumophilawas enumerated using the Legiolert assay. A total of 669 samples were analyzed during the study: 50 source water samples, 46 from the plant effluent, and 573 from the distribution system.L. pneumophilawas detected in two source water samples and not detected in any of the treated plant effluent samples.L. pneumophilawas detected in 14 distribution system samples, 13 from free chlorinated systems and one from a chloraminated system. All occurrences ofL. pneumophilawere observed when water temperatures were >18°C. Concentrations ofL. pneumophilawere <10 most probable number/100 mL except when chlorine residuals were less than 0.1 mg/L. Based on the results of this study, it is recommended that water utilities maintain at least a 0.1 mg/L chlorine residual, particularly when water temperatures are >18°C.
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