Water main replacement decisions may be based on arbitrary criteria such as age or on historic operating records and the experiences of a utility. Use of the latter method enables a utility to analyze leak and break patterns and to develop rehabilitation‐replacement plans. The author provides an overview of the causes of water main breaks and leaks and then describes several studies in which water main breaks have been analyzed in terms of pipe age, geographic location, or diameter.

Disinfection by‐product concentrations in a transmission system can change in response to downstream treatment processes. Semimechanistic models that describe the formation of disinfection by‐products (DBPs) (including trihalomethanes and haloacetic acids) were developed for the Massachusetts Water Resources Authority, an unfiltered surface water system using chlorine. The model's parameters were hydroxide concentration, chlorine decay kinetics or chlorine reacted, ultraviolet light absorbance at 254 nm, and algae concentration. One of the challenges in estimating or predicting DBP concentrations is that treatment processes at various points in the transmission system have substantial effects on the factors that affect DBP formation and rates of DBP formation. This article describes the formation of total trihalomethanes and haloacetic acids in the Massachusetts Water Resources Authority system and takes into account three treatment processes within the system. Coefficients used in the model were based on monitoring data collected from October 1997 to July 1999 and were validated with monitoring data from August 1999 to January 2000.

Many utilities do not appreciate the fact that routine breaks of metal water mains often result from deterioration caused by gradual external corrosion. The author outlines the basic terms and conditions of galvanic and electrolytic corrosion, summarizes case studies that illustrate causes of external corrosion of underground metal mains and that describe methods to control external corrosion, and discusses the role of soil in external corrosion. Critical research needs identified include prolonging existing main life, identifying and controlling electrolytic corrosion problems, and evaluating the economics of corrosion control for new mains.

Massachusetts Water Resources Authority started adding sodium hypochlorite to its raw water (Wachusett Reservoir) in September 1997 to achieve compliance with the requirements of the Surface Water Treatment Rule for unfiltered surface water supplies, mainly the 3‐log C × T (concentration times time) value for Giardia inactivation. There were concerns about the chlorine dosage necessary to achieve pathogen inactivation and the effect of that dosage on the amount of disinfection by‐products (DBPs) formed. Weekly chlorine decay tests were initiated in April 1998 to gather information on chlorine decay so that the necessary parameters to produce an integrated C × T value could be developed (area under the chlorine decay curve). Wachusett Reservoir water quality is also affected by transfer of water from the Quabbin Reservoir, which has lower total organic carbon and UV254 absorbance levels. A model was developed to describe the rate constant as a function of hydroxide concentration (taking both pH and temperature effects into account through the ion product of water), UV254 absorbance, and chlorine dose only. The availability of kinetic parameters allows development of a method for calculating C × T achievement for primary disinfection. Models for DBP formation will be presented in another article. These models together allow for better determination of the necessary chlorine dosage to achieve the required C × T value and minimize DBP formation.

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