EPA believes that if these contaminants are present in your water at levels above these standards, the contaminants may cause the water to appear cloudy or colored, or to taste or smell bad. This may cause a great number of people to stop using water from their public water system even though the water is actually safe to drink. Secondary standards are set to give public water systems some guidance on removing these chemicals to levels that are below what most people will find to be noticeable. Additional information on drinking water standards is available at http://water.epa.gov/drink/standardsriskmanagement.cfm.
Why does EPA set National Secondary Drinking Water Standards?
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