By Karen S. Garvin
Mechanical filters are used to remove leaves and other debris from water. They also remove dirt, silt and clay particles from the water. Mechanical filters may be made from metal screens, fabric, ceramic or paper. Sediment in water is unpleasant but not usually a health risk. Most home water filtration units use replaceable paper filters that screen out fine sediment.
BACTERIA AND PARASITES
Filtering water is essential to keep harmful bacteria and parasites from the drinking water supply. Giardiasis is an illness that causes severe diarrhea leading to weight loss and dehydration. A person with giardiasis may be sick for up to six weeks. The microscopic parasite that causes the disease is Giardia intenstinalis, an organism that can survive in the environment for many months. It can be ingested from water that has become contaminated with animal or human feces. Another parasite that can cause similar symptoms is cryptosporidium. Cryptosporidium is resistant to chlorine and must be filtered out with mechanical filters.
Most municipal water utility companies use chlorine to treat drinking water because it is inexpensive, easy to use and highly effective at killing many of the bacteria found in water. It can also eliminate some viruses. While it is a good disinfectant, chlorine can make drinking water smell and taste unpleasant, and it can also react with some metals to form hazardous compounds. An activated carbon filter removes the chlorine smell and taste from water.
Lead is toxic when ingested, and it’s necessary to remove lead from drinking water. Lead commonly gets into drinking water when it seeps into the water supply from old plumbing pipes or the solder used to join them together. Lead can be removed from water through reverse osmosis filters, distillation and carbon filters designed specifically to remove the metal. Health agencies recommend that people who rely on well water have their wells tested at least once a year for lead and other contaminants.
PESTICIDES AND CHEMICALS
Pesticide residue in drinking water may be on the rise because the organic pesticides widely used today are soluble in water and can easily get into the water supply. Before the 1940s most of the pesticides routinely used contained heavy metals that did not readily dissolve in water. Activated carbon filters can remove pesticides and volatile organic compounds from drinking water.