- This data was created based on the measurements of radioactivity concentrations in the drinking water by water Suppliers / local governments conducted by the Nuclear Regulation Authority (MEXT till April 2013) and ten prefectures near Fukushima Prefecture (Miyagi , Yamagata, Niigata, Ibaraki, Tochigi, Gumma, Saitama, Tokyo, Kanagawa and Chiba Prefecture) released to the public in the Ministry of Health, Labour and Welfare website. The measurements have been conducted since March 2011 in ten prefectures near Fukushima Prefecture.