When a public water system samples the water to test for metal contaminants, should the samples be taken before or after the water has been treated?
Systems that use ground water must take a minimum of one sample at every entry point to the distribution system that is representative of each well after treatment. Systems that use surface water or a combination of surface water and ground water must take a minimum of one sample at every entry point to the distribution system after treatment or in the distribution system at a point that is representative of each source after treatment (40 CFR 141.23(a)(1) and (2)).
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