Phosphates are extensively used in detergent formulations and washing powders. Phosphates also find widespread application in the food processing industry and in industrial water treatment processes. Agricultural fertilizers normally contain phosphate minerals and phosphates also arise from the breakdown of plant materials and in animal wastes.

Phosphates can therefore enter water courses through a variety of routes - particularly domestic and industrial effluents and run-off from agricultural land. Phosphate is an important control test for natural and drinking waters.

Whilst phosphates are not generally considered harmful for human consumption, they do exhibit a complex effect on the natural environment. In particular phosphates are associated with eutrophication of water and with rapid unwanted plant growth in rivers and lakes. Phosphates present in natural water pass through into drinking water supplies.

The YSI Phosphate LR test provides a simple method of measuring phosphate levels over the range 0 - 4 mg/l (PO₄). For drinking water the EEC has set a guide level of 0.5 mg/l PO4 (0.4 mg/l P₂O₅) and a maximum admissible concentration of 6.7 mg/l PO₄ (5 mg/l P₂O₅).