Water treatment is performed in order to improve water quality. The processes employed for water treatment depend on the quality of the water supply. In all cases, water has to be disinfected in order to deactivate any existing microorganisms present in water. So far, this technique was proved to be the most important for the protection of human life. It is commonly done using chlorine or chlorine dioxide, and in many cases, other processes are also used such as ozonation and ultraviolet irradiation. If the water originates from a surface water supply such as a river, lake, or dam, then the suspended particles are the most important problem. Different techniques to remove suspended particles include the addition of coagulants and the use of membranes. If the water originates from groundwater through mountain springs, usually, the water quality is good, and in most cases, only disinfection is required. However, if the water originates from groundwater wells, it may be rich in metals that need to be removed through chemical precipitation. Softening is another technique commonly used to remove hardness in case water is hard, which is performed by the addition of lime and subsequent precipitation of calcium as calcium carbonate and magnesium as magnesium hydroxide.