An investigation was conducted to determine the cause(s) of rapid pitting failure of galvanized steel pipe used in consumer plumbing systems. The presence of copper in water and the character of the galvanized steel pipe were factors examined in detail. Pipe manufactured in Korea, Australia, and in the U.S. were compared for pipe structure and zinc coating. In pilot testing, increasing copper concentrations (from 0.0 to 5.0 mg/L) produced increased corrosion activity on the pipe surface as measured by greater deposition of scale, calcium, iron, zinc, and copper. Also, the ratio of iron surface area to zinc surface area increased. Other factors, such as the mode of exposure and the addition of citrate, had no measurable impact. The corrosion activity, as measured by scale formation, was greatest on the Korean pipe, followed by the U.S. and Australian. Rapid pitting of the sort observed in several southern California homes did not occur under any of the conditions tested.