Fluoride failure: From Sandy City's water system incident to statewide ban and beyond

In 2019, a fluoride overfeed in the drinking water system of Sandy City, Utah, USA, sickened residents, corroded pipes, and released lead and copper. Sandy operators changed practices immediately, state water regulators issued administrative orders in following years, and in 2025, due partly to the incident and partly to national mood, the Utah legislature banned water fluoridation altogether—the first such ban in the United States. This case study examines the incident’s technical failures (in equipment settings, control logic, and hydraulics), procedural failures (in water sampling, record keeping, and public notification), and how changes in fluoridation practice and policy escalated from a single local event to the national stage. • A drinking water fluoridation system in Sandy, Utah, USA, failed in 2019. • This is the first peer-reviewed report of the incident. • The incident sickened users, corroded pipes, and released lead and copper. • Technical and procedural failures escalated during the incident. • In 2025, Utah became the first state to ban fluoridation, and others may follow.