AWWA JAW55965

This paper examines the relative effects of polyphosphates versus orthophosphates on tap water in pipes of various ages (three years, six months, and two weeks in age). Although orthophosphate dosing reduced soluble lead release by about 70% in most cases, increased lead release was observed in the new pipes. Hexametaphosphate increased soluble lead release over a broad range of water qualities, with each milligram per litre of residual hexametaphosphate increasing soluble lead release by about 1.6 mg/L, compared with orthophosphate. On the basis of these results and other researchers' findings, polyphosphate cannot be recommended for lead corrosion control. Polyphosphate still offers important benefits for preventing scaling and precipitation of iron or manganese and facilitating certain types of iron corrosion control. However, utilities may want to determine the minimum polyphosphate dose that achieves these goals because detriments to maximum soluble lead in pipes during stagnation are proportional to the residual polyphosphate.