Water filters work by disinfection methods, filtration, reverse osmosis, distillation and ion exchange to remove harmful impurities. Each process has its advantages and kills specific types of contaminates. Disinfection methods include using choline, boiling and pasteurization to kill bacteria that cause acute illness, and carbon filtration systems sift out sand, silt, clay and other organic material that has been suspended in the water, as noted by the University of Missouri Extension.
Reverse osmosis is a process where carbon or mechanical filters are used to remove any debris in water and then it is fed under pressure through a semi-permeable membrane. This process removes salt, minerals, organic and inorganic chemicals in large amounts, but the procedure discards 75 percent of the water being filtered as it contains contaminants.
Distillation heats the water, turns it into steam and purifies it from minerals, bacteria, organic chemicals and small amounts of metals as it recondenses. The distillation process is lengthy and only small amounts can be purified during one day.
An ion exchange, or water softener, treats water for hardness by removing calcium and magnesium, the chemicals that cause it. Water is directed through a tank where sodium is exchanged for the hardening compounds as well as iron and many heavy metals.