The rationale for dividing public water systems into three groups is the ______ of persons using the water.

• A. Pathogen exposure
• B. Possible cancer contaminant exposure
• C. Nitrate and nitrite exposure
• D. Chemical exposure

Answer: (D)

The main idea being tested is that public water systems are grouped according to the chemical exposure that people using the water may experience. This grouping reflects how different levels and types of chemical contaminants can affect health, so it helps guide monitoring, treatment, and regulatory actions. Chemical exposure covers a broad range of potential contaminants—from disinfectants and disinfection byproducts to inorganic and organic chemicals—so it provides a comprehensive basis for determining appropriate protections for users. Specific concerns like pathogen exposure focus on microbes and are addressed mainly through disinfection rather than broad chemical management. Nitrate and nitrite are only one subset of chemicals, and cancer contaminant exposure is a health risk that arises from various chemicals rather than a standalone grouping. Therefore, grouping by chemical exposure best explains why public water systems are divided into three categories.