Evaluation of Zinc Orthophosphate to Control Lead Solder Corrosion in Waters With High Chloride to Sulfate Mass Ratio

Chloride levels are increasing in some water supplies around the country due to use of road salts and seawater intrusion, which can increase the chloride-to-sulfate mass ratio (CSMR) and trigger serious water lead contamination from galvanic lead solder: copper pipe corrosion. Previous attempts to control this problem through simple water chemistry modifications were unsuccessful, but in this work a combination of zinc orthophosphate and moderate alkalinity mitigated lead release in testing at two utilities. Either zinc alone or phosphate alone were irrelatively ineffective, but the combination of zinc orthophosphate reduced lead leaching by 54-99% (compared to the control without inhibitors) if alkalinity was above about 55 mg/L as CaCO3. These results may help mitigate future lead in water contamination events.