The text start from here. Water Quality and Water Resources Storage Volume 80% of the water resources for Tokyo come from the Tonegawa and Arakawa River systems. Around 20% comes from the Tama River system. * Because the data are preliminary figures, those figures may be corrected at a later date. Water storage volume of the dams on the Tonegawa River system Click on the following chart to expand it. Water storage volume of the dams on the Arakawa River System Click on the following chart to expand it. Water storage volume of the dams on the Tamagawa River system Click on the following chart to expand it.