Why do water systems add phosphate to drinking water? What are the health effects of drinking water containing phosphates? 

Answer:

Public water systems (PWSs) commonly add phosphates to drinking water to prevent the release of metals in drinking water. Orthophosphate is most commonly used for lead and copper control. Polyphosphates sequester iron and manganese to prevent discolored water but are not effective to control lead and copper. Blended phosphates are a mix of orthophosphate and polyphosphate, which can potentially provide both sequestration and corrosion control. 

Orthophosphate is available as phosphoric acid, in salt form (potassium or sodium), and as zinc orthophosphate. Orthophosphate reacts with lead and copper to form compounds that have a strong tendency to stay in solid form and not dissolve into water. The extent to which orthophosphate can control lead and copper release depends on the orthophosphate concentration, pH, DIC, and the characteristics of the existing corrosion scale (e.g., whether it contains other metals such as iron or aluminum). 

Question (23002-32407)

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