To solve or prevent copper pitting problems, it is first necessary to achieve a clearer understanding of copper corrosion theory, parts of which are currently not supported by practical experience. Some current theories of copper pitting are contradicted by practical experience. Although it has been theorized that chloride initiates copper pitting attack, simple experiments show that the presence of chloride ion actually tends to decrease the likelihood that pitting will occur. In contrast, sulfate plays no role in pitting theory, yet sulfate has consistently demonstrated a propensity to initiate and propagate copper pitting. New theories are required to reconcile pitting theory and practical observation in order to allow the rational mitigation of copper pitting problems. In addition, the presence of natural organic matter (NOM) in water supplies prevents or inhibits certain copper corrosion problems. As a result, recent efforts to remove NOM as a means of controlling disinfection by‐products may lead to increased copper corrosion problems.

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Replacement of lead service lines can cause elevated lead levels immediately after construction, even after removal of the full lead source. Recent data collected by the District of Columbia Water and Sewer Authority in Washington, D.C., indicated that this can be partly attributed to lead release from iron corrosion scales on old, galvanized in‐home plumbing. This article summarizes a three‐part study investigating the phenomenon of capture and release of lead mobilized from an upstream service line by iron corrosion scales in galvanized plumbing. The study used profile sampling data from homes in the District of Columbia, corrosion scale analyses, and pipe‐loop experiments to examine whether iron corrosion scales can contribute meaningfully to drinking water lead. The study concluded that iron corrosion scales can be a persistent lead source, identified factors that can trigger release, and characterized potential long‐term effects.

Electrochemical kinetic parameters on copper plumbing surfaces were investigated under hydraulic and water quality conditions typical of distribution systems. The generally reported values of anodic and cathodic Tafel slopes were found to be inapplicable to plumbing surfaces of drinking water systems. Actual values may differ from reported values by up to twofold. Cathodic Tafel slopes vary strongly with the oxidant–disinfectant constituents of the water, whereas anodic slopes are influenced by corrosion inhibitors and aging of the corrosion scale. The corrosion current (corrosion rate) is affected by these and other parameters, including dissolved oxygen, pH, and chlorine residual. Contrary to some reports, orthophosphates were found to significantly reduce corrosion rates on copper surfaces; however, the phosphate scales that provide this protection are prone to rapid dissolution at low pH.

More and more utilities are using chloramines in place of free chlorine for greater residual stability and better compliance with both the Total Coliform Rule and the stringent requirements of the Disinfectants/Disinfection Byproducts Rule. However, new information about disinfectantinduced changes in oxidation reduction potential, lead and copper chemistry, scale formation, and scale destabilization involving natural organic matter has contributed to greater understanding of factors influencing increased corrosion and metals release. This article consolidates and updates information about potential effects of changing disinfectants on lead and copper release in drinking water distribution systems. The findings indicate the importance of chemical properties and electrochemical behavior in understanding how corroding metals and alloys respond to transition from free chlorine to chloramines and vice versa.