Influence of service reservoir construction age on the likelihood of bacteriological failure occurrence

Service reservoirs (SRs) are crucial components in drinking water distribution systems (DWDSs). These assets are often associated with water quality issues, including significant waterborne disease outbreaks. To ensure safety of supply, monitoring is conducted at SR outlets for disinfectant residual and bacteriological indicators. Older SRs are often believed to be a source of bacteriological failures as old or poorly constructed SRs can be prone to structural issues, which can lead to ingress and contamination of the stored water. However, there is a lack of evidence to support the existence of a genuine relationship between SR age and risk of failure. In this study, historical bacteriological failure data at SR outlets and company-wide SR construction age data collected from three large UK water utilities was used to assess the potential relationship between the duration of time a SR has been in service and the likelihood of bacteriological failure. Findings showed that there was no relationship between the two parameters. Analysis also revealed instances where newer SRs, no older than twenty years old, experienced one or more bacteriological failures, challenging the ingrained association that older SRs are at a higher risk of ingress and bacteriological contamination.