I am looking at a water report for my public water system. Under the contaminant heading for lead and copper there is a column heading titled 90th percentile. What does this column mean?
Answer: The Consumer Confidence Report must include the 90th percentile concentration of the most recent round(s) of sampling for lead and copper. If the “90th percentile” level is above the action level, this is called an action level exceedance. The action level is the concentration of a contaminant which, if…