|Water for Urban Areas (UNU, 2000, 243 p.)|
|2. Water management in Metropolitan Tokyo|
Conventionally, the concept of water resource developments was limited to the production of new water resources through river developments, including the construction of dams and estuary barrages. For now, and for some time to come, these conventional river developments will continue to be the main technologies. But the demand for and supply of water should be brought into balance by combining various developing technologies and not by depending on river developments alone.
Considering that water resources are circulating resources, water at every phase of circulation must be seen as a resource. In other words, water sources should not be limited to the water from rivers, lakes, and ponds and underground water, but should include all forms, from rainwater to treated sewage.
The utilization of treated sewage for building use and environmental use, which has already begun on a small scale in Tokyo, is a significant step in the long-term vision of future water resource policies. Though there are many problems with using treated sewage, such as cost, administrative matters, and the creation of laws, its utilization must become the most important task of the twenty-first century. There are many ways to attain this goal, such as sending treated sewage back to the upper basins of rivers, or sending it through underground pipes to wherever it is needed, as is being done in some areas already.
Using treated sewage has many advantages, including the facts that it enables the increase in water demand to be met, and that the production of treated sewage is carried out close to the place of water consumption. The utilization of treated sewage is a good way of increasing the rate of water recycling and thus contributing to the ultimate goal of efficient water utilization.
As far as the desalination of seawater is concerned, the costs of constructing and operating desalination plants are quite high, and energy consumption at plants is very high. Furthermore, for Tokyo it would be necessary to provide extremely long pipes into Tokyo Bay to get clean seawater. All these problems make the idea unfeasible for some time to come.
The development of water resources through conventional river projects is reaching its limits for large cities such as Tokyo. Dam sites are getting further away from consumption areas, and the effects of dam developments upon the natural and social environment have to be stringently watched. Consequently, the cost of measures to deal with environmental problems has made the cost of dam construction high.
Promoting awareness of water conservation among users will be an important part of water resources policies in the future. Since the development of water resources has become expensive and difficult, controlling the rise in water demand is vital. To this end, water users must be made aware of the fact that water is an invaluable resource and that it must be used sparingly. The use of water-conserving appliances must be expanded, and public relations activities must be reinforced. Such efforts should not be limited to water resource areas, but should become an essential measure in coping with the deterioration of the global environment.