Rainwater harvesting in Tokyo, Japan

Tokyo lies in the humid sub tropical zone. There is a rain season starting in early June and lasting till mid of July. Annual rainfall averages 1,380 mm (55 inches), with a wetter summer and a drier winter. Until 1990s, the main focus for application of rainwater harvesting was for domestic water supply. In 1994, the Tokyo international rain water conference was hosted in Japan. The siginificance of this conference is important as it represented a turining point in perceptions regarding the role, application and potenetial for rainwater catchment system technologies world wide. The rainwater havestingl played a vital role in solving water crisis in Tokyo and growing in megaities around the world, especially in Asia. In Tokyo and elsewhere in japan there has thus been much interest in the use of household water storage systems to provide water for fire fighting and other works. Such household resevoirs could also provide emergency domestic water supplies in the period immedietly following any major seismic events. Although rainwater is still not utilised much in Tokyo, there has been serious investigation into potential role that rainwater catchments systems could play in water supply, flood preservation and disaster mitigation stratagies.

A Sumo-wrestling arena in Sumida City utilizes rainwater on a large scale. The 8,400m2 rooftop of this arena serves as the catchment surface for the rainwater utilization system. The system drains the collected rainwater into a 1,000m3 underground storage tank and uses it for toilet flushing and air conditioning. Following this example, many new public facilities including the City Hall has begun to introduce rainwater utilization systems.

"Rojison", a simple and unique rainwater utilization facility at the community level in Tokyo, Japan

At the community level, a simple and unique rainwater utilization facility, “Rojison”, has been set up by local residents in the Mukojima district of Tokyo to utilise rainwater collected from the roofs of private houses for garden watering, fire-fighting and drinking water in emergencies.

To date, about 750 private and public buildings in Tokyo have introduced rainwater collection and utilization systems. Rainwater utilization is now flourishing at both the public and private levels.









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