The use of iodine contrast agents occasionally causes serious allergic symptoms including anaphylaxis. At Kyoto University Hospital to prevent nephropathy we began recommending water intake before and after administration of iodine contrast agents in September 2012. In the present study we investigated the effect of water intake on the incidence of allergy-like events after the use of non-ionic iodine contrast agents. We extracted the occurrence of allergy-like events from the incident report system in our hospital from January 2011 to September 2014, and classified these events into the following 3 grades: 1+ (follow-up); 2+ (medication treatment); and 3+ (hospitalization). The allergy-like incidence rate was calculated for subsequent evaluation according to season and water intake. Allergy-like events significantly decreased from 0.49% before the recommendation of water intake to 0.26% at 1 year and 0.20% at 2 years after implementing the recommendation. The incidence of allergy-like events was significantly higher in summer than in winter before water intake was recommended. After implementing the recommendation, the value for summer significantly decreased to an incidence similar to that of winter. Respiratory and gastrointestinal allergy-like symptoms were dramatically decreased after implementing the recommendation. Water intake may be useful for preventing allergy-like events associated with non-ionic iodine contrast agents, especially during the summer.