Phosphates naturally occur in living and decaying plant and animal remains as well as free ions and mineralized compounds in rocks, sediments and soil. However they are also introduced to the water supply through major man-made sources including  sewage, runoff from agricultural sites, and lawn fertilizers. It is commonly found only in very low concentrations in unpolluted waters. It is added to municipal water supplies as a corrosion inhibitor.

While phosphate is a dietary requirement, too much can cause health problems. Excessive amounts of phosphate has been linked to kidney damage and osteoporosis. It should be noted that too little phosphate can cause health issues as well.