The maximum contaminant limits in tap water:
radioactive iodine (I-131): 300Bq/L (300,000mBq/kg)
radioactive cesium(Cs): 200Bq/L (200,000mBq/kg)
Source: "Guide: Emergency Preparedness for Nuclear Facilities",
Nuclear Safety Commission, June, 1980- final revised in 2010
original info from : http://ftp.jaist.ac.jp/pub/emergency/monitoring.tokyo-eiken.go.jp/monitoring/w-past_data.html
