Chemicals are then added to remove soil and mud. Next, the water goes through a process which removes sediment particles from the water. Lime is added to soften the water, and carbon dioxide is added to stop the lime from softening. The water is filtered through sand and gravel. Depending on the level of nitrates, the water will then go though nitrate removal.
Chlorine is added to kill disease-causing organisms.
Finally, a fluoride treatment is added to help prevent tooth decay. Before, during and after this process, the water is repeatedly tested, says L.D. McMullen, Ph.D., CEO and general manager of the Des Moine s Water Works. Our water is contaminated for many reasons, and humans carry most of the blame. McMullen says agriculture is the biggest source of potential contaminants. Ninety percent of the nation's water supply is used for agricultural purposes, the other 10 percent for residential use.