The Legionella genus houses several opportunistic pathogens that cause legionellosis, which ranges from mild (Pontiac Fever) to severe (Legionnaires’ …

In recent years, health concerns about stagnant water in buildings have been raised. In some instances, elevated metal contaminant and opportunistic pathogen levels have been detected in stagnant building fixtures. Here, water quality in a large school building was monitored after it had been closed for six months and was reopened. Several chemical and microbial water quality parameters were elevated after the closure period. Some stagnant faucet water samples exceeded the U.S. federal drinking water limits for metals. Cold water from a kitchen fixture (21,949 μg/L zinc) exceeded the 6000 μg/L federal 1 day health advisory for a 10 kg child, indicating a health risk existed. Approximately 5% of the fixtures sampled tested positive forLegionella pneumophila; a drinking water fountain sample containedL. pneumophila at 1289.6 MPN/100 mL. In response, the building’s management implemented a shock disinfection procedure. After shock disinfection, total trihalomethane concentrations remained elevated, and two fixtures were found to be L. pneumophila positive, which did not test positive prior to the remediation. This study revealed that after prolonged building water system stagnation, certain contaminants can exceed drinking water limits and evidence-based guidance for building plumbing shock chlorination and remediation efficacy should be developed.