New targets for water supply works

Ever since the establishment of modern waterworks in Tokyo a hundred years ago, efforts have been made to secure water resources and to maintain facilities. These efforts have brought results at last, but it is no longer a question of just securing the necessary volume of water. A series of new problems has surfaced. To cope with these problems, in 1997 the Tokyo Waterworks Bureau proposed seven significant targets for the next quarter-century.

Waterworks that are immune to shortages

In recent years, there has been no shortage as serious as that of summer 1964. However, every few years, restrictions on water use have been imposed in periods of low rainfall. Because water is used in many diverse fields, the effect of water restrictions on citizens' lives and activities is quite serious.

The goal for Japan's waterworks is a stable supply of water even in times of great shortage that occur once every 10 years, but Tokyo's waterworks have not yet reached that level. The waterworks of San Francisco and New York in the United States have been designed to withstand the greatest historical shortages, and in London they are designed to withstand the shortage that occurs once in 50 years. The reservoirs on the Tone River and the Tama River for Tokyo's waterworks hold about 30 m³ per person. In comparison, the pondage per person is 520 m³ for San Francisco and 280 m³ for New York. The pondage is as low as 90 m³ per person for Paris and 35 m³ for London, but the Seine River, as the water resource for Paris, and the Thames River, as the water resource for London, experience little fluctuation in discharges, which has made a stable supply possible. Since the pondage per person for the Tokyo waterworks is quite small, it can be said that the safety margin of the water supply is not high. It is therefore important to establish a waterworks system immune from shortage.

Waterworks that can provide a constant water supply

Many disasters related to water quality have occurred in recent years - there were 299 cases in 1995. About 60 per cent of cases of water pollution are due to oil. In order to cope with the problem, channels for emergency communications and information collection have been established by the communications network through conferences held by related administrative organizations.

Disasters related to waterworks facilities, in particular purification plants, include pollution of water sources with toxic oils, ageing of the facilities, and electricity failure caused by lightning strike or snow fall. Disasters related to water pipes involve traffic vibration, ageing of pipes, leaks caused by soil corrosion, and damage from construction works such as road repairs or gas pipe works.

Even in times of disasters related to water quality or facilities, systems to ensure a constant water supply must be established.

Preparation for a great earthquake

The Hanshin-Awaji earthquake of January 1995 should be acknowledged as a precedent for epicentral earthquakes in Kanto urban areas. It is clear that Tokyo's dilapidated water pipes would be devastated if hit by such an earthquake. Since the Hanshin earthquakes, the Tokyo Waterworks Bureau has been proceeding with the reinforcement of reservoir, intake, purification, transmission, and distribution facilities against seismic shocks. In order to secure potable water in the event of an emergency, it is planned to locate water storage bases every 2 km. For this purpose, existing purification plants and water stations will be used as water storage bases. For areas that are more than 2 km from these purification plants and water stations, emergency water tanks are already in place; for example, there are 45 tanks in the Ward Areas and 7 tanks in Tama District. Each tank contains 1,500 m³ of water and is placed in a park that has been designated as a refuge. Within the Tokyo area, there are 169 emergency water supply points, and the total potable water volume constantly stored is 910,000 m³. This is equivalent to the consumption of Tokyo's 12 million citizens for three weeks, allowing 3 litres of water per person per day.

Taking into account the worst possible scenario at the time of an earthquake disaster, ways to secure potable water and water to extinguish fires must be sought.

Maintaining water quality

As regards Tokyo's future water management, measures to maintain the quality of the water must be seriously considered. The advanced water treatment started at the Kanamachi Purification Plant should not be considered as a temporary measure to cope with the contamination of water resources. It should be seen as the forerunner of measures at a time when many new and dangerous chemical substances are being developed.

Providing an impartial and efficient supply

In normal times, or even in times of disasters or shortages, the purpose of the water service is to provide an impartial and efficient water supply for users. Means of establishing such a system must be sought.

Waterworks that consider the environment

Waterworks must be designed to take into account energy saving, the efficient use of energy, and the recycling of resources at all stages such as purification treatment and the supply and operation of water services.

Waterworks that are familiar to users

In order to realize a peaceful life for the users, information collection from users and a give-and-take two-way information system must be encouraged. It is important for waterworks to become familiar and intelligible to its users.

Future water resources policies

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.