PROMOTING RAINWATER UTILIZATION

JFS Newsletter No.6 (February 2003)

Japan is an urbanized country. In particular, the Tokyo area, accounting for only 3.5 percent of the country's total land area, has about 26 percent of the entire population.

The more a population becomes concentrated, the more water use increases. The Tokyo area meets its water demand by drawing water from rivers and dams as far as 150 kilometer away.

On the other hand, with urbanization, more land is covered by asphalt and concrete in the form of roads, buildings, parking lots and other forms of cover, preventing rainwater from infiltrating underground. Most rivers flowing through cities are encased in cement and concrete, serving only as conduits of water to the sea..

In recent years, many cities in Japan started to suffer from "urban flooding": sewer backups and flooding of small- to medium-sized rivers when heavy rains fall. In one incident, a person was drowned by water overflowing into an underground shopping area. As one can see, urban flooding is a big issue for cities.

In many cities in Japan, rain that falls in cities is just channeled off to the ocean, whereas the water used in cities is drawn from remote dams, but ironically, they suffer from flooding during downpours. In short, cities that don't utilize rainwater and are vulnerable to the rain.

It is said that the Tokyo metropolitan area has an annual rainfall of 2.5 billion cubic meters. On the other hand, people in the area use about 2 billion cubic meters of water per annum. This means that the Tokyo area receives more rain than the amount of water it uses, but the rainwater is just channeled into sewers and then to the ocean. The ultimate irony was in 1994, when Tokyo suffered from flooding due to downpours during the same year that people were fussing about a drought.

On another note, water supply difficulties after the Great Hanshin-Awaji Earthquake in January 1995 raised the importance of securing water supplies from the viewpoint of disaster preparedness.

In Japan, an increasing number of organizations and municipalities has been turning to rainwater utilization in the last decade. Their aims include finding alternative water sources for drinking water, preventing urban flooding and securing emergency water sources for disaster-responses.

According to "Water Resources in Japan 2002" (Ministry of Land, Infrastructure and Transport, Water Resource Division), 934 facilities in Japan use rainwater for flushing toilets and other purposes. In particular, many local governments have started to promote rainwater utilization.

One example is the Kochi prefectural government. In 2001, they converted old septic tanks and heat storage tanks for air conditioning into rainwater tanks (330 tonnes) at main government buildings. They use rainwater from the rooftop and on-site springwater to meet almost 90 percent of the water demand of 40 tonnes per day needed for flush toilets in the buildings. The renovation cost was about 15 million yen (about U.S.$125,000,) but will likely be recovered within five years due to lower water bills.

Now more than 100 local municipalities participate in the "Rainwater Utilization Liaison Council for Local Governments," a network of local governments to promote to utilize rainwater in Japan. More than 30 local governments subsidize the installation of rainwater tanks.

One of the leaders in rainwater utilization at the local government level is the Sumida ward in Tokyo.

The Ryogoku Kokugikan, a building that houses Japan's primary sumo (Japan's national sport) ring in the Sumida ward, has a total area of 35,700 square meters, with three stories above and two stories underground. A 1,000-tonne underground tank stores rainwater from the rooftop and it is used for flush toilets and building cooling. In an emergency, the water in the tank can be used as drinking water.

In the Sumida ward, 26 public buildings, including the Sumida ward office have facilities to utilize rainwater. In this area, there are 9 regional rainwater utilization systems with underground tanks of 3 to 10 tonnes each. Local residents can pump up water by hand from the underground tanks for watering flowers in daily life and as water for fire-fighting and drinking in emergency.

The Sumida ward stipulated "guidelines for rainwater utilization in Sumida ward" in 1995, creating a basic rule to install rainwater utilization facilities for all newly constructed buildings in the ward.

The Sumida ward also aims to increase private "miniature dams" in the area by setting-up a subsidy framework for utilizing rainwater. So far, the installation of more than 160 facilities, mainly small-sized water storage tanks, have been subsidized.

In 2001, the Association of Businesses for Rainwater Utilization was founded. They are cooperating with architects involved in rainwater utilization to develop affordable and high-quality facilities and equipment for utilizing rainwater.

The Sumida ward held the "Tokyo International Conference on Rainwater Utilization" in 1994. Since then, it has expanded its scope of activities beyond the border. One of the deliverables of such efforts is publication of a booklet in March 2002, entitled "Rainwater Harvesting and Utilisation--An Environmentally Sound Approach for Sustainable Urban Water Management: An Introductory Guide for Decision-Makers." This is a booklet on policies and technology transfer of rainwater utilization produced collaboratively by Sumida ward, the UNEP International Environmental Technology Centre, and People for Promoting Rainwater Utilization. The booklet has been disseminated throughout the world via United Nations organizations and agencies.
http://www.unep.or.jp/ietc/publications/urban/urbanenv-2/12.asp

In 2001, Sumida ward renovated a closed primary school building and opened the Rainwater Museum, the first facility of its kind in the world. The organization People for Promoting Rainwater Utilization, serving as driving force for this museum, together with Sumida ward and the Association of Businesses for Rainwater Utilization, sees the Rainwater Museum as a first step toward information dissemination and is committed to make more efforts toward creating an International Center for Rainwater.