The effectiveness of a one-month switch from chloramines to free chlorine for control of nitrification and the consequences of this strategy were evaluated in three distribution systems. Nitrification was observed in two of the systems, and may have been influenced by greater loss of disinfectant residual in cast-iron pipe sections. Free chlorine inhibited nitrification episodes, though evidence of nitrification was observed several months after the return to chloramines. Ammonia-oxidizing bacteria (AOB) were found attached to pipe-wall specimens removed from a distribution system during and at the end of the free-chlorination period, suggesting AOB persisted during free chlorination. Consequences of disinfectant switching include breakpoint chlorination reactions that caused periods of low disinfectant residuals and increased total trihalomethane (TTHM) concentrations. The highest TTHM concentration might not be observed until long after the return to chloramines at locations with long residence time where free chlorine remains.

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Utilities with uncovered finished water reservoirs face many water quality, security, and regulatory challenges. These utilities will need to provide covered storage or treatment to comply with the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) requirements. This article provides an overview of the history of uncovered reservoirs, identifies drivers for improving protection of uncovered reservoirs, discusses options for compliance with the LT2ESWTR, presents an approach to decision‐making regarding compliance, and presents case studies that demonstrate how utilities have implemented various compliance alternatives. A variety of cover and treatment options are potentially appropriate for LT2ESWTR compliance, and many evaluation criteria must be considered when selecting a compliance alternative. It is recommended that each utility determine, prioritize, and rank its alternatives based on criteria that are specific to its regulatory compliance and project goals. Typical evaluation criteria include regulatory compliance, water quality effects, site aesthetics, operations and maintenance requirements, vulnerability/ public safety, cost, permitting requirements, and design life.