Chlorine is also one of the elements of the diatomic molecule (Cl2) and has been part of our daily lives for years. In the early history of chlorine, chlorine was first discovered in the 13th century and was first used by the Swedish chemist Carl Wilem Scheele mentioned in the introduction in 1774. The most serious threats to health would not be caused by chemicals, but by highly infectious organisms or bacteria present in the water we drink and use daily. Chlorine is a major disinfectant that is inexpensive and kills most serious pathogenic bacteria in water. However, chlorine disinfection generates a wide variety of byproducts. A class of chlorination byproducts, known as trihalomethanes (THMs), are suspected of being carcinogenic. Due to concerns about these byproducts in the water supply, chlorine is now kept at minimal levels and other disinfection methods are used more frequently. Chloramines form more stable disinfectants and have less risk of harmful byproducts, but cost more to use. Other methods focus on the removal of organisms through coagulation, sedimentation, and enhanced filtration. The functions of chlorination are to disinfect water or wastewater, decolorize water or fabrics, disinfect and clean surfaces, remove iron and manganese, and reduce odors. However, the odor of some compounds, such as certain phenolic compounds, is worsened by reaction with chlorine. Some soluble metals can be made insoluble by oxidation by chlorine (soluble Fe2+ is oxidized to insoluble Fe3+), making the metal easier to remove by sedimentation or