AWWA JAW17312

This article presents results of a study conducted to investigate the mobilization of heavy metals from plumbing systems in 55 homes in rural Nova Scotia that obtain water from wells. Samples of both running and standing water were taken daily from each home for three days. Metal mobilization of copper, lead, and zinc occurred in significant amounts from the plumbing systems of the homes sampled. In many cases this leaching caused concentrations of copper and lead to exceed Canadian drinking water limits within only a few hours of standing in the water pipes. Water samples containing copper and lead concentrations in excess of recommended limits were found in each of the four communities studied. On the average, concentrations of copper, zinc, and lead increased by factors ranging from 5 to 22 when water remained in pipes overnight. Correlation analyses confirmed that four indexes commonly used to assess the corrosive tendency of a water (namely the Langelier, Ryznar, and Aggressiveness indexes and CLSO) were not good predictors of the degree of metal leaching that could occur in a given water. The degree of copper and lead leaching was strongly related to the chemical composition of the water. Stepwise regression analysis helped identify twelve water chemistry variables as being related to the degree of metal mobilization observed. These variables included potassium, sodium, calcium, magnesium, and manganese; the chloride, nitrate, hydrogen, and sulfate ions; and dissolved oxygen and conductivity. No obvious relationship was found between the pH of the water and the degree of metal leaching, nor was the absolute amount of metal leached found to be strongly related to the age or length of piping, or to the length of time the water stood in the pipes. Because of the high concentrations of copper and lead found in samples of standing water, it is recommended that residents in homes with metal piping allow the water to flush for several minutes before use in the morning or if the water has not been used for several hours. Includes 41 references, tables.