Evaluation of Drinking Water Additives on Lead Solder Corrosion in Premises Plumbing
Naomi Lewis (Dalhousie University)

Although lead solder has been banned in Canada, it may still be present in old premise plumbing, causing risks to public health. Orthophosphate, sodium silicate, and free chlorine are common additives used in drinking water treatment for different purposes, yet their interactions with lead-containing solders are poorly understood. Orthophosphate, when added to drinking water, can prevent lead corrosion by forming a scale composed of low-solubility lead phosphate minerals. Sodium silicate is used to control iron and manganese precipitation. It has been investigated as a corrosion inhibitor; however, several studies show it can release lead into drinking water by dispersing particles. Free chlorine can decrease lead solubility by oxidizing lead II to lead IV, forming an insoluble lead scale, however, this treatment is limited due to the instability of lead IV species. Additionally, the chloride-to-sulfate-mass ratio CSMR must be considered since a ratio of greater than 0.5 has increased lead release in galvanic systems.

This experiment aimed to compare the effects of free chlorine, orthophosphate, and sodium silicate on the release of metals from simulated pipe joints using tin-lead solder and copper pipe using a 23 factorial design. Experiments were conducted with synthetic water with moderate alkalinity, high CSMR ~0.7, low water hardness, and a pH of 7.5. This study suggests that orthophosphate and free chlorine may be beneficial for the reduction of lead release from tin-lead solder. This study is relevant for addressing ongoing concerns about lead release from solder in premise plumbing, on which little research currently exists, and potential treatment options to reduce the risk of lead poisoning from drinking water.