The public health issues associated with water quality typically focus on drinking water. Technologic advances in watershed protection, drinking-water treatment processes, and drinking-water distribution system management and protection have improved the CDC's ability to ensure that most waterborne agents responsible for human illness are removed and/or inactivated. The CDC is fully involved in addressing the critical public health issues of exposure assessment, definition of adverse health outcomes, biomonitoring, and illness prevention.

• As part of the treatment process, drinking water may be disinfected to reduce microbial contamination. However, the disinfectants (e.g., chlorine) can react with organic matter in the water, producing disinfection by-products (DBPs). CDC is conducting studies that focus on different components of the public health impact of DBPs.
   
• The association between the quality of water used in food production and subsequent transmission of human illness is not completely understood. CDC is investigating the relative importance of irrigation source water and methods, the sanitary conditions on farms, and the hygienic practices of harvesting crews on microbial contamination of produce items that are usually eaten raw.
   
• Many chemical contaminants present in drinking water sources, such as pesticides or naturally-occurring toxins, are not removed by standard drinking water treatment processes. Some of the relevant projects include the following:
   
  • A multiphase project to assess the extent of human exposure to blue-green algae toxins in drinking water and to identify potential human health outcomes associated with these exposures.
     
  • An investigation of human exposure to methyl-tert butyl ether (MTBE) in drinking water that has been contaminated by gasoline spills and storage tank leaks.
     
  • An investigation of the extent of human exposure to arsenic in tap water.