Background - On January 12, 2011, a drinking water supply system in a building in Rennes housing a shopping and business center was contaminated with ethylene glycol (EG). An investigation was conducted to document exposure to EG, assess its health effects, and evaluate compliance with a recommendation against drinking the water. Method - Information regarding the building occupants’ awareness of the contamination, the amounts of water consumed, and the occurrence of clinical symptoms was collected via a questionnaire administered to the occupants. The results of analyses of EG levels in the water were used to construct two scenarios for the evolution of EG levels and to calculate EG exposure doses. Results - A total of 204 people responded to the questionnaire. Almost all (96.7%) of the individuals were notified of the contamination, including 10.8% as early as January 12. More than one in two people consumed water during the contamination period. Among these, the geometric means of EG intake were 8.9 mg/kg or 6.4 mg/kg, depending on the case. One-quarter of the people who consumed water during the contamination period reported experiencing at least one symptom consistent with EG poisoning. Conclusion - The calculated exposure doses exceed the toxicological reference value for EG. An earlier and more widespread alert would likely have reduced the number of people exposed. (R.A.)