• Treatment of surface water involves a multi-barrier approach.reservoir overflow image by Paula Gent from Fotolia.com
  
  Water conveyance systems that provide water to fifteen service connections or regularly serve twenty-five individuals for sixty days are considered public water systems and regulated by the Environmental Protection Agency (EPA). Before delivery to the public, surface water is treated in a series of steps. Surface water is far more likely to become contaminated by harmful substances than groundwater. Groundwater usually requires little to no treatment because it is less susceptible to contamination.
  
  

Surface Water

• Surface water is exposed to a variety of harmful contaminants and must be treated before delivery. Runoff from agriculture, parking lots, and untreated sewage are common sources of contamination. Disease-causing organisms such as Giardia, Cryptosporidium, and bacteria are a primary concern. A sequence of processes removes microbes, bacteria, and other types of contamination. Pretreatment begins with physical barriers to catch large debris. Chlorine and potassium permanganate or ozone are added to treat seasonal turbidity and algal growth. Chemical feed, rapid mix, and flocculation follow pretreatment. Alum, ferric chloride, or synthetic polymers are added as coagulants, and the water is vigorously mixed. Other chemicals are added to adjust pH. Rapid mixture of the water and coagulants neutralizes particles and forms the "floc," which is then removed. Larger floc particles settle to the bottom and are periodically collected for landfill disposal. Lighter particles are removed from the rest of the water by filtration. Filtration media is specially designed to remove any remaining biological or inorganic particles. If necessary, disinfection occurs as the final step of the process.
  
  

Groundwater

• In rare cases, groundwater may require treatment for naturally occurring arsenic, fluoride, and nitrates. However, if man-made chemicals, such as solvents, fuels, and pesticides, make their way into the water and the source of contamination is not removed, the water must be treated. Water "hardness" is commonly treated with resin-coated media, allowing ion exchange with the calcium or magnesium causing the hardness. Iron and manganese removal is accomplished either by oxidation or brought out of solution with chlorine or potassium permanganate. Hydrogen sulfide gas can cause an odor and make water otherwise unpalatable. Gases are removed by chlorine or ozone. Some volatile organic compounds can be removed from groundwater by simple aeration.
  
  

Home Water Treatment

• A variety of home water treatments are available to consumers. Carbon filtration removes most organic compounds causing bad odor or taste. Carbon filters can be installed at the point where water enters a home, such as under sinks or on faucets, or on pitchers. Fiber filters can be purchased in a variety of weaves. Fiber filters with the smallest weaves are most effective but need frequent replacement. All carbon and fiber filters must be replaced regularly. Reverse osmosis and distilling units, which require electricity to operate, are the most expensive types of household treatments. Water softening units are often purchased for home water treatment neutralizing filters, and chemical feed pumps are also available to neutralize pH. Finally, chlorine is commonly used as a disinfectant. Any aftertaste from chlorine will be removed by a carbon filter.