The (UHL) and the University of Iowa Center for Health Effects of Environmental Contamination (CHEEC), in collaboration with the Iowa Department of Natural Resources (DNR) Drinking Water Section, used existing databases and special monitoring efforts to conduct a statewide assessment of ground water quality and its relationship to certain public health outcomes. The study looked at the occurrence of ammonia, nitrite, nitrate and nitrifying bacteria in selected public water supplies. The study also included the linkage of analytical data maintained by the UHL and CHEEC, IDNR and health outcome data maintained by the Iowa Registry for Congenital and Inherited Disorders and the State Health Registry of Iowa. The study examined exposure to certain water contaminants and the incidence of various health outcomes at the community level. The study goal was to provide the State of Iowa with an ecological assessment of the occurrence and concentration of ammonia, nitrite, and nitrate-nitrogen in community water supplies and the risk for adverse health outcomes including, low birthweight, certain birth defects and certain cancers. Results of the investigation showed that systems with elevated ammonia concentrations in their source water had elevated nitrite and nitrate concentrations in their distributions systems. The results also indicated that bacterial growth, even with chlorination, was sufficient to lead to the reduction of ammonia and thus contribute to nitrite and nitrate concentrations in the distribution system. No adverse health outcomes, associated with the contaminants of concern, were identified in the study because of an insufficient study population. The report made several recommendations related to monitoring for ammonia and nitrite, as well as control of scaling and biofilms in water supply distribution systems.