1. A salt that contains phosphorus as PO43-. 2. A product of the hydrolysis of condensed (polymeric) phosphates, i.e., the most hydrated or reverted ("broken down") and stable form of phosphate compounds. Orthophosphates cannot sequester metal ions and hardness, but they can form passivating films on anodic sites to suppress electrochemical corrosion reactions in metallic plumbing. 3. A nutrient required for plant and animal growth.