The Six Steps to Purifying Water

Most of the public relies on public water systems for their supply of water. Before water enters public treatment plants, it is typically contaminated with parasites and bacteria. The water is also is polluted with chemicals, oils, trash, and human and animal waste. Needless to say, that can make you pretty sick or even kill you. How the water is treated varies according to the size of the facility, the source of the water and its overall quality.

Purification Process

• Water must be gathered from a source. This is called the intake process. Over a third of the public water supply in the U.S. is sourced with water from the ground. Usually, groundwater comes from wells that can be anywhere from 50 to 1,000 feet deep. Most groundwater meets the government requirement for safety and does not require treatment. However, the remainder of the public receives water from community or public water systems, which must undergo a treatment process.

  Sources of water for eventual public consumption include lakes, reservoirs and rivers. The federal Environmental Protection Agency and states require that water taken from these supplies goes through a purification treatment. The preliminary treatment usually consists of coagulation. Chemicals, such as aluminum, iron salts or synthetic organics are added to the waste water. This forces small particles to bunch together.

  The water is then sent through a "bar screen." The bar screen removes debris like sticks and rags as the waste water flows down to a grit tank. Gravel, sand and objects that are not caught by the bar screen settle to the bottom of the container and are then removed. The water flows into a primary settling tank where the sedimentation process begins. Solids sink to the bottom of the tank; grease and oil gravitate to the top. These items are removed and the water is ready for filtration.

  The water must pass through filters that are comprised of sand, gravel and charcoal. This system removes tiny particles, including clays, silts, natural biologic matter and other impurities. The filtration procedure gives the water clarity. This process also makes the disinfectant techniques more effective. Disinfectant is necessary to ensure that any potential ly dangerous microorganisms are destroyed.

  The treated water is stored in reservoirs, which are called clear wells, or in closed holding tanks. Chlorine, chloramines, ultraviolet, chlorine dioxide or other disinfecting agents are used to sanitize the water at the treatment plant and in the water pipes leading to homes and businesses. Once the remaining microorganisms and germs are eliminated from the water, dechlorination may be necessary. Sodium bisulfite is added to the water to remove excess chlorine. The treated water is referred to as the "final effluent."