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Treatment Processes

Conventional surface water treatment plants have a fairly standard sequence of processes. After screening out large objects like fish and sticks, coagulant chemicals are added to the water to cause the tiny suspended particles that make the water cloudy to be attracted to each other and form “flocs.” Flocculation—the formation of larger flocs from smaller flocs—is typically achieved using gentle, constant mixing of the water to encourage particles and small floc to “bump” into each other, stick, and form larger floc. Once the flocs are large and heavy enough to be settled, the water moves into quiet sedimentation or settling basins. When most of the solids have settled out, some form of filtration either with sand or with membranes typically occurs. Disinfection is usually the next step. After disinfection, various chemicals may also be added to adjust pH, to prevent corrosion of the distribution system, or to prevent tooth decay. Ion exchange or activated carbon may be used during some part of this process to get rid of inorganic or organic contaminants. Groundwater sources generally have higher initial quality and tend to require less treatment than surface water sources.

Point-of-use and point-of-entry devices are typically simpler and employ a limited number of technologies. In most developed countries pathogen-free drinking water that meets international standards is available at every consumer’s tap. That being said, a significant number of consumers in the developed world elect to install point of use or point of entry devices as an extra precaution or to improve the aesthetic properties of the water in the public water system. In many parts of the developing world, however, public water systems that provide pathogen-free water are not available and success is measured primarily by reduced risk of diarrheal or other diseases. Thus, a point-of-use technology that is appropriate for one location is not necessarily recommended for another.

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