The effect of zinc orthophosphate and pH-alkalinity adjustment on metal levels leached into drinking water

Abstract

A 12-month pilot plant study was conducted to evaluate a number of corrosion control treatments to reduce metal leaching from typical household plumbing materials. A pipe loop system was used to test six treatment options, with a control loop of the characteristically soft, acidic, Greater Vancouver Water District (GVWD) water. Four pH- alkalinity combinations and two concentrations of zinc orthophosphate (0.37 mg/L and 1.0 mg/L as Zn) were studied. at regular intervals, the flowing, treated, and control waters were allowed to stagnate in the pipe loop system for 8- and 16-h periods. Following the designated standing time, water samples taken from the lead/tin solder jointed, soft copper plumbing coils, the submerged, free standing coils of 50/50 lead/tin solder, and the brass faucets, were measured for lead, copper, and zinc levels. Overall, when compared to the control loop, the pH-alkalinity treatments appeared to exacerbate metal leaching in standing samples. The zinc orthophosphate treated loops were both effective at reducing lead and copper leaching to below control levels. In general, the two standing times showed little difference in the levels of leached metals. The exception to this occurred in the higher dose zinc orthophosphate loop, which had higher copper and zinc levels at the longer standing time. Key words: copper, corrosion, drinking water, lead, zinc orthophosphate.