Tokyo metropolis, the capital of Japan and the most populated metropolitan city in the world. It lies in the Kanto region on the southeastern side of the main island Honshu and includes the Izu Islands and Ogasawara Islands. With an area of 2,188square kilometer, has a population of 13,185,502 (August 2011). The population of the city is about 10% of the national population, and is divided into the 23 Wards and the Tama Area. Tokyo lies in the humid subtropical climate zone with hot humid summers and generally mild winters with cool spells.
There are five primary rivers that flow through the Tokyo basin: the Tonegawa, Arakawa, Tamagawa, Sagamgawa, and Tsurumigawa. This area is flood prone and sits at a low elevation. Approximately 1.5 million of Tokyo’s residents reside below sea level (Carmin, 2011).
Groundwater is the important source of water resources in Tokyo although it was not managed systematically as in other cities of Japan. Issues related to water table depletion, land subsidence, sea water intrusions were major groundwater problems during 1950s and 1960s. However, due to enforcement of several laws such as “Industrial water Law” and “Building Water Law” land subsidence problem is almost at control. The contaminations from domestic wastewater or fertilizers were also identified, but introduction of water purification plants or sewerage plants have been effective in these case. Other major concern was due to VOCs contamination such as trichloroethylene and tetrachloroethylene produced before 1980s. Prevention of VOC has been successful to some extent, however once contaminated it takes longer time to improve the condition. (IGES 2007)