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

City	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)
Sapporo	1,706	314	381	785	1,194	4,826
Sendai	922	382	460	463	1,266	2,824
Kawasaki	1,193	437	509	1,026	587	2,135
Yokohama	3,310	399	486	1,780	587	8,406
Nagoya	2,146	386	478	1,424	570	4,990
Kyoto	1,426	485	619	980	700	3,598
Osaka	2,603	580	729	2,430	772	4,993
Kobe	1,504	415	503	833	762	4,172
Hiroshima	1,091	382	490	644	576	3,627
Kita-Kyushu	1,018	360	441	710	751	3,544
Fukuoka	1,214	296	386	705	927	3,372
Tokyo	10,928	430	513	6,960	791	21,484