Chemical precipitation or reagent coagulation precipitates impurities from purified water via change of pH, electrooxidizing potential or coprecipitation using precipitating agents (coagulants) such as ferrous or aluminum sulphates. Reagent oxidation is a special case of reagent coagulation in which oxidizing reagents (e.g., potassium permanganate or bichromate) are added in purified solution to destroy organic impurities or to change the valence of multi-valent ions following precipitation.