The quality of water in public supplies varies from place to place, so you may want to have your water tested for impurities. Some chemicals in the water are naturally-occurring, while others are added by local water companies. Chlorine and lead (LED) are two common sources of problems. Chlorine may result in birth defects, cancer, and heart disease. Lead can be especially harmful to young children, causing organ damage, mental retardation and stunting the nervous system. Some public water supplies may contain microbes that could be dangerous to people whose immune systems aren't functioning properly. Fluoride (FLOOR-ide) in your drinking water can be beneficial in preventing tooth decay, especially in children. However, you don't want it to contain more than two parts per million. Should you decide you wish to purify your water at home, there are several different kinds of filtration systems available. They vary greatly in price and type of method used. Some of the various methods are steam distillation, carbon filtration, ion-exchange, reverse osmosis, and purifiers that use ultraviolet light.