If the consumer's water is delivered by a municipal water utility, suggest that they contact the water utility and ask for a copy of the Municipal Drinking Water Contaminant Analysis Report. The list should detail the EPA MCLs and the levels found in the water at the treatment plant. Tell callers that they should compare the results of the water utility against the EPA list to identify potential or actual problem contaminants. The consumer needs to understand that these results can be trusted and that the only parameters that may change are lead, copper and Cryptosporidium or Giardia cysts. Lead and copper may leach into the water after it leaves the water treatment plant, and if the community is known to have elevated levels of these contaminants, the consumer may want to have water from the house tap analyzed by an EPA Certified drinking water analysis laboratory.
Cysts are another matter altogether.
If cysts are a concern, a water filter is probably in order. If callers have private wells, refer them to the local health department to identify typical well water contaminants in the area and the names of laboratories certified to analyze local drinking water samples. After contacting the lab and submitting samples, the consumer can compare the lab's results with the EPA's MCLs. The NSF Consumer Listing Book of NSF Certified water filters includes a list of the contaminants with MCLs. NSF has tried to help consumers choose appropriate products by developing a Consumer Listing Book that organizes Certified products by manufacturer claim rather than by standard.