Assessing the effect of distribution system O&M on water quality

Historical water quality variations were evaluated in several distribution systems using a data integration approach. Utilities from three Canadian cities, two European cities, and two US cities participated in the study. The approach discussed here combines the use of water quality, system operations and maintenance (O&M) data, a hydraulic model, and a geographical information system. Temporal, spatial, and hydraulic proximities among occurrences were achieved through database queries. This investigation included: 140 coliform-positive samples in five distribution systems; 48 occurrences of heterotrophic plate count (HPC) bacteria in four systems; and 217 customer complaints from three systems. The objective of this research was to identify the main causes of water quality variations to eventually determine the proportion attributable to O&M activities. The results showed that the role of O&M activities in the occurrence of coliforms in distribution systems varies, explaining 9-45% of coliform cases investigated in each system. O&M work was associated with about 30% of customer complaints investigated in each of the networks studied, and its association with HPC events was negligible in three out of four systems. Although O&M activities benefit water quality in the long term, greater understanding of their short-term negative effects could better prevent and control potential water quality degradation.