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This study compared sodium silicate and zinc orthophosphate for their ability to decrease lead and copper release from pilot-scale premise plumbing in low alkalinity (<5 mg/L CaCO3) water. The study used pipe loops (to age the water) connected to copper pipe rigs. The copper pipe rigs were constructed using 50:50 lead:tin solder, which provided the only source of lead. Three different treatments were compared, using the same source water: phosphate (0.8 mg-PO4/L at pH 7.3), sodium silicate with pH control (18 mg-Si/L at pH 7.3), and sodium silicate (18 mg-Si/L at pH 6.3). Lead and copper levels (both total and dissolved) were measured following the copper pipe rig after two different stagnation times (24 h, 30 min). The phosphate treatment consistently resulted in significantly lower lead release compared to sodium silicate at the same pH of 7.3. The phosphate treated pipe rigs released 12 μg/L and 2 μg/L lead following the 24 h and 30 min stagnation times, respectively. The sodium silicate with pH control system released 46 μg/L and 6.7 μg/L lead following 24 h and 30 min stagnation time, respectively. The sodium silicate treated pipe rigs released 27.4 and 4.6 μg/L lead following the 24 h and 30 min stagnation time, respectively. The phosphate treatment also consistently released less copper than both the sodium silicate with pH control treatment and the sodium silicate treatment. However, more lead particles were observed in the phosphate treatment compared to either of the sodium silicate treatments. The difference in performance between the sodium silicate corrosion inhibitor at two different pH levels, suggests that the performance of sodium silicate could be further optimized.

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