Jar tests and a circulating water system were used to evaluate the effect of water quality parameters, in particular the Langelier index (SI), on the corrosion of galvanized steel. Since waters with a positive SI were sometimes found to be at least as corrosive as waters with a negative SI, especially if the effect of dissolved oxygen was neglected, no definite relationship could be established between corrosion rate and SI. In both Gainesville, Fla., tap water and deionized water, corrosion was observed to be fastest in the pH range 5-6.5. A general mechanism for the formation of corrosion products is presented. Overall results suggest that the SI should be used only with caution in the practice ofcorrosion control and that prediction of a water' s corrosivity should also consider the influence of other water quality parameters.Iron and steel pipes are usually coated on the corrosion of galvanized-iron with zinc to protect them from extensive structure+ have received considerable corrosion damage. Since the introduction attention. Investigations have been conof galvanized pipe, one of the oldest and ducted on the fundamentals of zinc cormost common plumbing materials used rosion, such as the electrochemical in drinking water systems, zinc has been behavior of zinc5 and the natural pitting reported in water supplies,' and studies of its crystals,6 as well as the effect of TABLE 1anions.4 However, little is known about the effect of some water quality factors on the corrosion of galvanized pipe in potable water systems, including the nature of the corrosion products formed. Further understanding of the corrosive reaction of water on galvanized pipe is needed to help water treatment plant operators produce a less corrosive treated water. For instance, because the US Environmental Protection Agency (USEPA) has implicitly recommended the use of the Langelier index (calcium carbonate [CaCOs] saturation index) by utilities to monitor the corrosive potential of process water, the effect of the Langelier index on the corrosion of zinc in galvanized pipe should be thoroughly evaluated.