Following the crisis at the Fukushima Daiichi Nuclear Power Plant caused by the 2011 Tohoku earthquake and tsunami, radioactive substances (131I, 134Cs, 137Cs) were detected in tap water throughout eastern Japan. There is now concern that internal exposure to radioactive substances in the dialysate could pose a danger to hemodialysis patients. Radioactive substances were measured in three hemodialysis facilities before and after purification of tap water for use in hemodialysis. Radioactive iodine was detected at levels between 13 and 15 Bq/kg in tap water from the three facilities, but was not detected by reverse osmosis membrane at any of the facilities. We confirmed that the amount of radioactive substances in dialysate fell below the limit of detection (7–8 Bq/kg) by reverse osmosis membrane. It is now necessary to clarify the maximum safe level of radiation in dialysate for chronic hemodialysis patients.