Cover Image
close this bookWater for Urban Areas (UNU, 2000, 243 p.)
close this folder2. Water management in Metropolitan Tokyo
View the document(introduction...)
Open this folder and view contentsHistory of waterworks in Tokyo
Open this folder and view contentsThe present situation
Open this folder and view contentsThe future
Open this folder and view contentsWater circulation and urban civilization
View the documentAcknowledgements


Yutaka Takahasi

Early water supply systems

During the sixteenth and seventeenth centuries, the city of Edo was already equipped with comprehensive water supply systems that did not exist even in Europe. This was one foundation of the prosperity of Edo that has lasted for nearly 300 years. In 1590, Tokugawa Ieyasu ordered Okubo Fujigoro to draw up a master plan for a water supply system, and, based on this master plan, part of the Kanda Canal was completed. In 1654, the Tama River Canal, with a length of 43 km, was completed by using the Tama River, running west of Edo. It became possible to supply water continuously to the centre of the Edo area and its vicinity. These excellent water systems were based on what one might call classical technologies. They depended not on pumps but on the skilful use of gravity flow, and the water was not sterilized. A rough chronological table of waterworks in Tokyo is shown in table 2.1.

Table 2.1 History of waterworks in Tokyo


Tokugawa Ieyasu, founder of the Edo Shogunate, commissioned Okubo Fujigoro to carry out a survey and draw up a master plan; partial completion of the Kanda Canal


Completion of the Tamagawa Canal


Yodobashi Purification Plant started operating


Facilities badly damaged in the Great Kanto earthquake


Sakai Purification Plant started operating


Completion of Kanamachi Purification Plant


Completion of Yamaguchi Reservoir


Construction of Ogouchi Dam started


Facilities devastated in World War II


Completion of Ogouchi Dam (Tama River system)


Nagasawa Purification Plant started operating


Higashi-Murayama Purification Plant started operating


Great water shortage in the Tama River system; water distribution cut by max.50%


Abolition of Yodobashi Purification Plant because of the Shinjuku Suburbanization Plan


Asaka Purification Plant started operating


Completion of Yagisawa Dam (Tone River system)


Completion of Shimokubo Dam (Tone River system)

Completion of Tone Diversion Weir and Musashi Canal


Ozaku Purification Plant started operating

Intake stopped from Tamagawa Purification Plant


Completion of Tone Estuary Barrage


Misono Purification Plant started operating


Completion of Kusaki Dam (Tone River system)


Misato Purification Plant started operating


Completion of Naramata Dam (Tone River system)


Completion of 1st Stage of Advanced Water Purification Treatment Facility in Kanamachi Purification Plant

Completion of Tamagawa Cold Water Countermeasure Facility

Source: Bureau of Waterworks (1994).

Opening of modern waterworks

Fig. 2.1 Developments in Tokyo's water service, 1900-1995 (Source: Bureau of Waterworks, 1994)

Along with the opening of the country, the Japanese government imported advanced waterworks technologies developed in Western Europe. Beginning in 1887, modern waterworks were constructed under the supervision of William Palmer, an Englishman, in Yokohama, which had a large settlement of foreigners. The Yodobashi Purification Plant started operating in 1898. At the beginning, it was capable of supplying only 166,800 m3 of water per day to 80,000 people. However, as the population increased and the potable water service spread, the waterworks kept on growing. Private sector systems and nearby villages and towns were absorbed. Developments in Tokyo's water service are shown in figure 2.1; the growth in the average daily water supply is shown in figure 2.2.

These figures demonstrate the remarkable expansion of the water supply system. The process of expansion was not smooth, however. Some of the difficulties were the Kanto earthquake on 1 September 1923, World War II, and in particular the destruction of waterworks by air raids towards the end of the war, and then slow recovery. Furthermore, serious water shortages in the Tama River in 1940, flood damage in the eastern areas of Tokyo caused by Typhoon Katherine in 1947, and another serious water shortage caused by low precipitation on the Tama River Upper Basin in the summer of 1964 affected the management of the Tokyo water service.

The reconstruction of the water service facilities that had been completely destroyed by the earthquake of 1923 not only employed earthquake-resistant structures, but also involved the construction of new reserve water systems, changing from steam pumps to electric pumps at the Yodobashi Purification Plant, the carrying out of land readjustment for urban renewal, and major modifications to and expansion of water service networks. As a result of the unusual water shortages in the Tama River in 1940, water supply sources were reinforced, new wells were constructed, neighbouring water systems were connected, and emergency measures for water supply were completed.

Fig. 2.2 Growth in the average daily water supply volume, 1900-1995 (Source: Bureau of Waterworks, 1994)

The Ogouchi Dam project

As a drastic measure to cope with the rapid increase in population, the Tokyo City Waterworks Bureau decided to go ahead with the Ogouchi Dam project. At 149 m, the dam height was, as a dam for the exclusive use of the water service, the highest in the world at the time, and it was an epoch-making undertaking considering that the highest dam in Japan at the time was the Komaki Dam, at 79 m. The water volume of the reservoir (later named Lake Okutama) created by the Ogouchi Dam was approximately 180 million m3. However, construction did not commence until 1938, because the acquisition of water rights in the lower basin of the river ran into difficulties. Moreover, construction had to be discontinued during World War II because of a shortage of labour and materials.

After the war, construction of the dam recommenced in 1948, and it was completed in 1957. The water supply capability of the Tokyo waterworks immediately expanded. Within a year, the Nagasawa Purification Plant, intended for bringing water from the Sagami River to Tokyo, was completed. This was built in Kawasaki City in Kanagawa Prefecture, which is next to Tokyo. The ceding of the water supply to Tokyo began in 1959. Also in 1957 the Waterworks Laws were decreed. The promotion of the water service was a significant policy throughout the Japan.

War damage and the increase in water leakage

World War II not only interrupted construction of the Ogouchi Dam, but caused great damage to the waterworks facilities. Air raids became ever more intense over all Japanese cities from 1944 and were heavily concentrated on Tokyo in particular; its waterworks facilities were completely devastated. From August 1945, with the end of the war, reconstruction of the war-damaged waterworks facilities began. Since losses of water from water pipes in Tokyo had been considerable as a result of the war damage and poor maintenance, the repair of water leaks became the main challenge.

Table 2.2 Trends in Tokyo's water leakage rate, 1915-1995


Rate (%)































Source: 1950-1995 – Bureau of Waterworks, Annual Report on Waterworks in Tokyo, Tokyo Metropolitan Government.

Changes in the rate of water leakage since 1915 are shown in table 2.2. The leakage rate had been over 20 per cent since 1930, but in 1945 - at the end of the war - it had rocketed to approximately 80 percent. Though it fell to 68 per cent by 1946, the water supply system was jokingly called the "waterworks colander." Specialists in the Metropolitan Government were employed to find the points of leakage and to deal with the problem. They succeeded in at last bringing the rate down to 22 per cent in 1955. This rate was still quite high. As a result of continued efforts, it fell to 10.6 per cent in 1993. Since the annual distribution of water in 1993 was 1,700 million m3, a leakage rate of 10.6 per cent meant that the volume of leakage was 170 million m3 annually, an amount equivalent to the total pondage of the Ogouchi Dam. However, since most of the points of leakage were not in the main pipes, but in the very great number of final distribution pipes, it was not easy either to locate or to deal with the problem; it required time and labour. It took many years to get the rate down to 10 per cent, and ceaseless efforts must continue to be made in the future.

Serious water shortage in 1964

From around 1957, when the Ogouchi Dam was completed, the population of Tokyo started to increase rapidly. This was a time of transition from a period of urban population concentration to a period of high economic growth. The population increase and the rise in living standards resulted in an inevitable increase in the consumption of potable water and the volume of water used for various city activities. For that reason, the annual increase in the water service in Tokyo reached approximately 300,000 m3.

In 1963/64, during this period of rapid increase in demand for water services, there was little precipitation in the upper basin of the Tama River, the upstream region of the Ogouchi Dam. In particular, precipitation during May and July of 1964, the rainy season, was extremely low. At this time, the sources of water for Tokyo consisted of the Tama River system, including the Ogouchi Dam (about 60 per cent), the Edo River (about 20 per cent), the Sagami River (about 10 per cent), and underground water and other sources (about 10 per cent). Dams along the upper basin of the Tone River, such as the Yagisawa Dam, were under construction, and others were still in the planning stage, so water from these areas was not yet supplying the water service system to serve the citizens of Tokyo. The lack of precipitation in the upper basin of the Tama River system lasted from June until 20 August 1964, and the pondage of Ogouchi Dam, which was 180 million m3 at its maximum, fell to as little as 2 million m3. This was a decisive blow to Tokyo's water supply. The Tokyo Waterworks Bureau had to impose severe restrictions on the use of water. Areas in the highlands of Tokyo went whole days with no water. Water tankers of the Self Defence Forces were mobilized every day, and citizens had to wait in line with buckets for their share.

The Olympic Games, held for the first time in Asia, were to open on 10 October 1964. A construction rush had been under way in Tokyo for hotels, metropolitan expressways, the Tokaido Shinkansen, and subways. Construction sites and newly built hotels were also suffering from the shortage of water.

Because the dams along the upper basin of the Tone River were not yet completed, the construction schedule for the Musashi Canal (a man-made channel connecting the Tone River and the Ara River) was accelerated. As part of the total water system carrying water to Tokyo, it succeeded in achieving a temporary supply of water by 20 August. Luckily, toward the end of August, normal precipitation for the season fell in the upper Tama River basin, and restrictions on water use were gradually lifted. The Olympic Games went ahead without any water-related fears.

Development of water resources in the upper Tone River basin

Development of the water resources of the upper basin of the Tone River system to serve Tokyo had been proposed to Tokyo City Council in 1926. Concrete discussions in the Council started in 1936, but it was not until after World War II that the actual plans were approved for execution. In March 1963, a plan to bring water from the Tone River to Tokyo was decreed by the Cabinet as the "Water Utilization Plan of Tone River Systems." Based on the plan, the development of water sources has become a part of the National Water Resource Development Plan, and many of its projects have been executed by the Water Resources Development Public Corporation that was established in 1962. The Tokyo Metropolitan Government was to take partial financial responsibility for the costs of the water supply, including industrial water, by way of multi-purpose dams. The Akigase Intake Weir and Asaka Canal had been built as emergency measures during the "Tokyo Water Famine" of 1964 as described earlier. The Musashi Canal was also constructed by the Public Corporation. Thus it became possible to get water from the Tone River systems when there was some spare volume, until the completion of dams in the upper basin of the river. Water from the upper Tone River basin was planned to flow through the Musashi Canal, via Tone Oseki (Tone Grand Diversion Weir), to the Ara River, with purification occurring at the Asaka Purification Plant, and sent from there to Tokyo by way of water pipes. The Asaka Purification Plant was completed in 1966. (Prior to that, in 1965, the Yodobashi Purification Plant, which had played an important role as the largest plant in Tokyo, ceased to exist. The site occupied by the plant was taken over for the development of the Shinjuku Suburbanization Plan, and became a town of high-rise buildings, such as the Tokyo Metropolitan Government Centre, hotels, and offices.)

The volume of water supplied to Tokyo increased by 1,200,000 m3/day after construction of the Asaka Purification Plant (900,000 m3/ day) and the Higashi-Murayama Purification Plant (300, 000 m3/ day). All planned construction was completed by 1968, including the Yagisawa Dam in the upper basin of the Tone River in August 1967 and the Shimokubo Dam in the basin of the Kanna River, a branch of the Tone River, in November 1968. As a result, the volume of water supplied to Tokyo increased dramatically. Furthermore, the Tone River water resource development projects were completed one by one, and after 1965 the water supply operation expanded to serve not only the urban areas of Tokyo but also Tama districts. Construction of the Tone Estuary Barrage was completed in 1971 and dams in the basin of the Watarase River, the Kinu River, etc. and expansion of the Asaka Purification Plant were undertaken in the 1960s and 1970s.

Since the 1970s, however, it has become increasingly difficult to get agreement on dam-site areas. Difficulties in balancing water demands in the future have been anticipated. The Tokyo Waterworks Bureau made a public announcement in 1973 on "Statements Concerning Water Conservation" and, for the first time, appealed to citizens regarding the need for control over water demand and the saving of water. At about the same time, the state government began to propose a "water conservation conscious society." Furthermore, the 1973 "Act of Special Measures for Reservoir Areas," a measure to cope with the difficult situation of upstream reservoir areas, was passed by the Diet. Great progress has been made, by making a differentiation from money compensation-type measures. This was one of the turning points in the history of dam construction policy.

Criticisms about dam construction were originally based on the shortcomings of the measures for the reservoir areas of the upstream basin. Eventually, the effect of dam construction upon the environment has begun to be taken into account, with the cost of environmental measures being added on. The cost of construction has thus risen considerably. Although the Yanba Dam and other dams along the Agatsuma River (a branch of the Tone River) are already on the government's construction list, potential dam sites are in general decreasing and it is gradually becoming difficult to secure future water resources for Tokyo by means only of dams.

Tokyo's waterworks, having experienced a century of many complications, have fulfilled their mission well. Now there are new problems: environmental problems such as pollution of water at intake points on rivers, etc., further upgrading of service to inhabitants, and earthquake measures.

General view

The waterworks of Tokyo have become a gigantic and complicated system supporting a modern megalopolis with a population of 12 million. In this section, present-day conditions will be outlined and comparisons made with other cities in Japan and with some of the major cities of the world.

The water resources of the present Tokyo waterworks are based on three major river systems, namely the Tone River system (80.2 per cent), the Tama River system (16.7 per cent), and the Sagami River (2.9 per cent), and underground water (the remaining 0.2 per cent). Classification of these, in relation to the purification plants, is shown in table 2.3. Most of the dams and purification plants relating to the Tone River system development were completed after the latter half of the 1960s, and these supply most of the water requirements of the citizens of Tokyo.

The dams in the Tama River system and Tone River system, used for supplying water, are listed in table 2.4. In addition to the Ogouchi Dam in the Tama River system, three reservoirs were constructed in the 1920s and 1930s; these store water taken from Intake Weir of the Tama River system for a short period of time, and send it to the Higashi-Murayama and Sakai purifying plants. In 1996, the main distribution pipes were 2, 009 km in length, and the small pipes were 19,887 km in length, giving a total length of 21,896 km (see table 2.5).

Table 2.3 Purification plants for Tokyo's water supply

Water resources

Purification plant


Contribution (%)

Treatment method




Tone River system





Rapid Sand Filtration


Partial Advanced Water Treatment




Rapid Sand Filtration





Rapid Sand Filtration





Rapid Sand Filtration





Rapid Sand Filtration Rapid Sand Filtration



Tama River system





Rapid Sand Filtration





Slow Sand Filtration





Slow Sand Filtration





Slow Sand Filtration




Rapid Sand Filtration


Slow Sand Filtration

Sagami River system





Rapid Sand Filtration


Underground water





Chlorine feeding



6, 959.5



Source: Bureau of Waterworks (1994).
a. Production at the Tamagawa Purification Plant has been halted because of pollution of the Tama River.

Table 2.4 Dams in the Tama River and Tone River systems


Effective capacity (lO3m3)

Catchment (km2)



Height (m)

Length (m)


Murayama-kami Reservoir



Earth dam with impervious wall




Murayama-shimo Reservoir



Earth dam with impervious wall




Yamaguchi Reservoir



Earth dam with impervious wall




Ogouchi Reservoir



Non-overflow straight concrete dam




Fujiwara Dam



Gravity system




Aimata Dam



Gravity system




Sonohara Dam



Gravity system




Yagisawa Dam



Arch system




Shimokubo Dam



Gravity system




Kusaki Dam



Gravity system




Watarase Reservoir



Pit-type reservoir




Naramata Dam







Source: Bureau of Waterworks (1994).

Table 2.5 Features of Tokyo's water service, 1984/5-1993/4





Population served (103)





Rate of service coverage (%)





Distribution pipe length (km)





Facility capacity (103m3/day)





Gross annual supply (106m3)





Maximum daily supply (103m3)





Average daily supply (l03m3)





Source: Bureau of Waterworks (1994).

One of the important tasks of today's purification plants is to produce water that is safe and tastes good, no matter how polluted the original supply. In particular, the Kanamachi Purification Plant, where the water comes from the Edo River, was no longer able to supply safe and palatable water with the use of the conventional rapid filtration system. A mouldy smell had been noticed in the water since around 1972, and filtering the water through powdered activated carbon had been tried without satisfactory results. Hence, an advanced water purification treatment system combining ozone, biochemical, and activated carbon treatments has been employed. This system is capable of treating 520,000 m3 (approximately one-third of the plant's total daily capacity of 1,600,000 m3). In order to cope with a similar problem that started in 1994 at the Misato Purification Plant, where the water is also taken from the Edo River, the same advanced water purification treatment system is under construction to exclude ammonia-based nitrogen gas, which is the cause of the smell of mould and bleach.

Since the pollution of river water has developed, advanced water purification technologies have been sought, and the cost of water purification has risen. Similar problems can be observed in Osaka's waterworks, where pollution is becoming serious in its water sources: Lake Biwa and the Yodo River.

In order to meet changes in the social environment appropriately and to respond promptly to diversified needs, new technology is developing. Currently, the most important areas are: the development of purification technology; improvement of the transmission and distribution system; improvement of the direct supply system; improvement of leakage prevention technology; and the effective utilization of resources and energy.

Industrial water

Industrial water started to be supplied in Tokyo at the time of high economic growth when the demand for industrial water was rapidly increasing. It started in the Kotoku District in 1964 and the Johoku District in 1971. The problem of land subsidence due to pumping an excessive amount of underground water had been serious in these eastern areas of Tokyo. In order to stop the pumping of underground water, industrial waterworks were constructed as a substitute. These measures, in place since 1975, have been seen as one of the main reasons for the cessation of subsidence in the eastern areas of Tokyo.

However, since demand for industrial water has been decreasing since 1974, owing to the relocation of factory sites, water conservation policies, etc., some of the water has been converted to use in incineration plants, for car washing, and for flushing toilets. Even so, the volume of industrial water use is still at excessive levels, and the accounts of the industrial water industry have continued to be in the red. Along with the problem of ageing facilities, a complete restructuring of the operation must be sought.

Utilization of treated sewage

The increase in the volume of sewage is proportional to the increase in water demand. The rate of coverage of the sewerage system in Japan passed 50 per cent in 1995. Japan is still a developing country as far as sewage is concerned. However, if one considers just the Ward Areas in Tokyo, the rate is now 100 per cent.

Treated sewage is beginning to be utilized for a variety of purposes, including toilet flushing (but not for drinking water). Treated sewage has also been utilized to cope with the exhaustion, even in normal conditions, of the Tamagawa Canal and the Nobidome Canal, which were constructed in the Edo period. A daily volume of about 43, 000 m3 has been transferred from the sewage treatment plant in the upper basin of the Tama River into the Nobidome Canal, starting in 1985, and into the Tamagawa Canal, from 1986. Since 1984, a maximum daily volume of 8, 000 m3 of treated sewage from the Ochiai Sewage Treatment Plant has been supplied to the Shinjuku Subcentre Area, where the Yodobashi Purification Plant used to be located.

Furthermore, since 1995, treated sewage has been utilized to supply water, at a rate of 1 m3/sec, to the Shibuya River, the Meguro River, and the Nomi River, where the volume of flow in normal conditions has shown a marked decrease.

The biggest cause of the decrease in flow in these streams, at normal times, has been the spread of the sewerage system. The sewerage system in Tokyo is designed to cope with heavy rain of 50 mm/hour. Consequently, most rainwater is drained through the sewerage system, and drainage by small streams has become unnecessary, even at times of heavy rain. In other words, most of the surface flow has been transformed into underground flows.

It is ironic that the treated sewage from sewage treatment plants has been put back into these streams in order to maintain their environmental balance, when discharges have decreased markedly because of the spread of the sewerage system. In some cities in Europe, small streams have been revived by discontinuing the use of sewerage systems. Sewerage systems have been a symbol of civilization, but this is no longer the case. One's view of twenty-first-century civilization is now affected by the flow of treated sewage into streams that have lost much of their original water volume.

Towards a ''water conservation conscious city''

In 1973, the "oil shock" created economic confusion throughout the world. Japan, having been seriously affected, has since then employed energy conservation as a state policy.

In January 1973, in order to balance water demand and also to control it, the Tokyo Waterworks Bureau publicly announced its "Policy to Control Water Demand," which was a forerunner for cities across Japan. At that time, despite the increase in water demand in Tokyo, water resource developments were not progressing according to plan, owing to popular movements against dam construction. Future water supply shortages were therefore anticipated.

For 80 years, with the constant increase in public water demand, the bureau had been planning and executing water resources development projects. This new policy was a great turning point in Tokyo's water demand planning. Furthermore, in Japan the supply of drinking water is a financially independent business within each city. Considering the fact that controlling demand meant less revenue, this was a drastic change of policy in the Waterworks Bureau.

At about the same time, a "water conservation conscious society" was proposed by the water administration of the state government. Such a policy was becoming popular all over Japan under the influence of cities such as Tokyo where water consumption was high.

In 1987, learning a lesson from the water shortages of that year, a Round-table Committee for Creating a Water Conservation-Conscious Society was formed within the Waterworks Bureau. The committee's report states the need to make urban society aware of the need for water conservation through the reinforcement of conventional water conservation systems and the philosophy of water recycling. Since then, the Waterworks Bureau has been actively promoting public relations activities to develop awareness of water conservation among citizens in their daily lives. It has also been requesting manufacturers to develop fixtures such as faucets, toilets, and laundry machines that conserve water.

Concerning the promotion of efficiency in water use, since 1984 there have been individual building recycling, district recycling, and large area recycling. Treated sewage and industrial water have begun to be utilized as their water resources.

As part of its leakage preventive measures, the Bureau makes it a rule to carry out repair work on the day that a surface leak is found. Where the leak is underground, the potential leakage volume is assessed by the minimum flow measurement method, and leaks are located with electronic leak detectors, correlation-type leak detectors, etc. (all performed at night-time). As a result, the leakage rate was reduced to 16.1 per cent in 1977 and to below 10 per cent in 1995 (as shown in table 2.2 above). The target is to bring the rate down to 7 per cent by the beginning of the twenty-first century. To prevent leaks, ductile metal and stainless steel are being used for water distribution pipes.

Tokyo's water service compared with other cities in Japan and the world

Tokyo, the capital of Japan, is the biggest city in Japan. It covers an area of 2, 183 km2, which is 0.6 per cent of the total national land area. Its population of a little short of 12 million is 9.5 per cent of the total national population. Its population density of 5,500 persons/km2 is about 17 times the national average.

Table 2.6 Features of the water service in Japan's main cities, 1994


Population served (103)

Average daily supply per person (litres)

Maximum daily supply per person (litres)

Water supply facility capacity (l03m3/day)

Household rates (yen/10m3)

Length of distribution pipes (km)





















































































Source: Bureau of Waterworks (1994).

Table 2.7 Features of the water service in various cities of the world


Population served (103)

Length of distribution pipes (km)

Length of distribution pipes per 103 people served (km)

Maximum daily supply per person (litres)











Cape Town



































Source: Bureau of Waterworks (1994).

Its water service population, waterworks capacity, and volume of water distributed are compared with other major Japanese cities in table 2.6. The maximum daily consumption of water per person in some of the major cities of the world is compared in table 2.7. Compared with Tokyo, the water supply volume of Detroit in the United States is very large, whereas in other cities consumption is lower. This reflects differences in attitudes and habits toward the use of water in each city. Nevertheless, in the face of severe environmental problems, every city should make efforts to save water.

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.

Rapid urbanization and changes in water circulation

Urbanization affects water circulation. The spread of sewerage systems, as described previously, caused a deterioration in river and canal environments as a result of water flow loss. Other changes in water circulation are caused by the paving of roads and the conversion of farmland into housing.

The urbanization of Tokyo started in the 1950s. Tokyo's population increased rapidly from the latter part of the 1950s into the 1960s, and is now some 12 million, warranting the name "mega-city." Urbanization at such a pace has changed the water circulation of Tokyo drastically, and has become the cause of new urban flood hazards. The Kano River typhoon, on 26 September 1958, produced the highest recorded rainfall per day (392 mm) since 1875 in Tokyo, and caused great flood damage in the newly developed housing areas of the western part of Tokyo. Since then, damage caused by rainfall has increased in parallel with new housing developments. Changes in water circulation during heavy rains are the main cause.

The urbanization of Tokyo has been accompanied by the populace's desire for a higher standard of living, resulting in a heavy burden on rivers and water circulation. These burdens have involved the control of water, the utilization of water, the environment, and the landscape. Embankments became taller as a result of river improvement works undertaken to protect against water hazards, thus spoiling views along rivers and streams. The construction of highways to provide easy access to the areas alongside these rivers has also spoiled riverside scenery.

In today's Tokyo, projects that aim to restore the rivers and water circulation of the city are finally under way. They include advanced water treatment systems in purification plants, the discharge of treated sewage into rivers and streams, the utilization of treated sewage in high-rise buildings, the encouragement of urban renewal work, and river improvement work in the development of the Super Embankment along the Sumida River - a river that is emblematic of Tokyo.

The philosophy of recycling

Urban developments that contribute to the convenience of urban life and economic efficiency have altered the nature of water circulation in Tokyo. As a result, the populace has been troubled by new types of flood hazard since 1985, a decrease in water bodies, a decrease in the ability to control the temperature in the city, and the heat island phenomenon, which has become acute in recent years. Tokyo waterworks have eagerly sought to meet the increased demand for water and have developed water resources by means of dam construction. New technologies, based on visions worthy of the twenty-first century and not limited to conventional planning ideas, have been sought for the water management of the future.

This could be called the materialization of the philosophy of recycling. The characteristics of water as a natural resource are intrinsic in the meaning of the recycling of resources. The utilization of treated sewage in buildings and to recharge rivers since the latter half of the 1980s in Tokyo, no matter how limited, should be recognized as the forerunner of water recycling measures from the point of view of the history of technologies.

New technologies must be developed to cope with the utilization of treated sewage, which is expected to grow in volume in Tokyo in the future. In order to achieve this goal, it is important to offer water of acceptable quality at low cost. The administration that produces treated sewage and the administrative bodies for waterworks, rivers, and streams, and the environments expected to use the treated sew- age are related to each other. In order to realize the philosophy of water recycling, an all-around administration is a must. In order to achieve this academically, the development of interdisciplinary fields of studies and cooperation is required. At the moment, treated sewage is sent underground from treatment plants to buildings, rivers, and water channels. For the future, however, studies are already under way on numerous technologies for sending it back to the upper basins of rivers and streams supplying purification plants.

In this context, the utilization of treated sewage must be recognized as one part of water resource development. Water resource development for big cities in the future should be a combination of dams, the utilization of treated sewage, the use of rainwater, as is being done in Sumida District, Tokyo, the conversion of existing water rights, etc. The designers and the executors of development plans must recognize that projects that do not take recycling into account affect the natural circulation of water in that area. If this concept is not accepted, the philosophy of recycling will not be able to be applied to Tokyo as a basic element in city planning.

The concept of recycling should not be limited to the waterworks of Tokyo; it should be applied to the water management of any future megalopolis and especially to the future planning of water-related infrastructure. As water-related projects become bigger and more complicated, the concept will expand its influence beyond borders. Hence, the concept is undoubtedly the key to the global problems of water and the environment.


I am grateful to Mr. Isao Tahara, an engineer with the Waterworks Bureau of the Tokyo Metropolitan Government, for collecting the data on waterworks in Tokyo, and to Mr. E. Marui and Mr. S. Konda, engineers with Construction Project Consultants, Inc., for their English language assistance in preparing this article.


Bureau of Waterworks. 1994. '94 Waterworks in Tokyo, Tokyo Metropolitan Government.

——— 1996. Annual Report on Waterworks in Tokyo, Tokyo Metropolitan Government (in Japanese).

Japan Waterworks Association. 1996. Statistics on Waterworks in Japan (in Japanese).