The amount of soluble lead in SW increases with:

• A. Increasing sulfates
• B. Decreasing hardness
• C. Increasing hardness
• D. Increasing phosphates

Answer: (B)

Lead solubility in water is strongly affected by water hardness, which comes from calcium and magnesium ions that help form a protective calcium carbonate scale on pipe surfaces. In harder water, this scale limits corrosion and keeps lead from dissolving into the water. When hardness decreases, the protective layer is thinner or absent, so lead can corrode more easily and ends up more soluble in the water. While additives like phosphates can reduce soluble lead by forming insoluble lead compounds, and sulfates don’t provide the same protective effect as hardness, the clearest relationship is that soluble lead increases as hardness falls.