Phosphorus occurs in natural water and wastewater almost solely as phosphates. It is a common constituent of agricultural fertilizers, manure, and organic wastes in sewage and industrial effluent. It is an essential element for the growth of plants and animals and in lake ecosystems. But excessive amount of phosphorus in water can lead to eutrophication resulting in reduced stability of the ecosystem. Phosphorus concentrations can be measured by colorimetric determination by stannous chloride method or ascorbic acid reduction method.