Abstract: During a staff training in a resort in Beijing conducted by an insurance company from 28 to 30 August 2010, a food poisoning event occurred after lunch and supper on 29 August. The etiological detection was conducted, the result indicated that 3 samples were positive for Proteus mirabilis, 1 was positive for Vibrio parahaemolyticus and 1 was positive for Enteropathogenic Escherichia coli O44:K74, which demonstrated that the food poisoning was caused by contaminated source water. The restaurant didn't get approval of supervision administration before starting service, and the design defect existed in water supply system, which resulting in the cross contamination of water used for different purpose.