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Water is delivered from a groundwater or surface water source to a treatment plant, where it is first aerated
to allow volatile gases to escape. Next, small particles are clumped together through the use of coagulating agents and allowed to settle out of the water. Particles that do not settle out
through coagulation slowly filter out to the bottom of a mazelike settling tank in a process known as sedimentation. The material at the bottom, called sludge, often creates a disposal
problem, since it may contain some toxic elements. Next, water flows through long horizontal tanks with filters made of gravel, sand, or granulated activated carbon and is collected at the
bottom of these filters. Filtration removes additional particles and bacteria. Finally, chlorination or other disinfectants kill any remaining microbes.
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DRINKING WATER TREATMENT
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Source: Raymond Gabler and the Editors of Consumer Reports, Is Your
Water Safe to Drink? (Mount Vernon, NY: Consumers Union, 1989), 330–333.
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