The effect of the chloride‐to‐sulfate mass ratio (CSMR) on lead leaching from 50:50 lead–tin solder galvanically coupled to copper in stagnant conditions was examined using bench‐scale testing and data from water utilities. The CSMR was significantly altered by coagulant changeover, blending of desalinated seawater, anion exchange, and NaCl brine leaks from onsite hypochlorite generators. Consistent with previous experiences, increasing the CSMR to the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead–tin solder galvanically coupled to copper. Before implementing any treatment changes that could increase the CSMR, utilities may want to use the protocol described in this article to ascertain the relative effect of the changes on lead corrosion.

As stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and the copper. If the resulting galvanic current exceeds about 2 μA/cm(2), a highly corrosive microenvironment can form at the solder surface, with pH < 2.5 and chloride concentrations at least 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface, and contributing to lead contamination of potable water supplies. The total mass of lead corroded was consistent with predictions based on the galvanic current, and lead leaching to water was correlated with galvanic current. If the concentration of sulfate in the water increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated.

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