A fluoride overfeed occurred at a well site near an elementary school in Portage, Michigan. The incident resulted in a high concentration of fluoride (92 milligrams per liter) in drinking water at the school. Seven students who drank water from the school fountain reportedly suffered nausea and vomiting. Toxicological evaluations were made by conducting a risk assessment. On the basis of the symptoms experienced by the students, it was concluded that the fluoride had irritated the stomach causing nausea and vomiting. This mild oral exposure to fluoride was, however, deemed too low to cause any long-term appreciable adverse health effects. Despite subsequent flushing, the concentration of the fluoride in the drinking water remained variable during the first nine days after the incident. With several flushings over the 48 days after the incident, the concentration of fluoride was brought down to optimal levels. The electrical circuit that energized the fluoride system was modified to prevent another overfeed. In addition, operational changes were made to further minimize the impact of such an overfeed.