Water is a vital resource that we all too often take for granted. If a major earthquake strikes Tokyo, the capital could see its water infrastructure damaged severely, preventing needed water from reaching residents and potentially creating millions of “water refugees.” A look at the situation.
Aging Waterworks a Disaster in Waiting
When the Noto earthquake claimed the lives of over 200 people on New Year’s Day, 2024, collapsed buildings and tsunami devastation reminded us of the awesome power of earthquakes. The loss of water has also caused hardship for Noto residents. A large swathe of Ishikawa (110,000 dwellings in 16 different municipalities) lost water as a result of damage to water mains and treatment plants. Residents displaced by the earthquake struggled to access drinking water, and use of toilets was limited, as was laundry and bathing. In fact, as of late March some areas remained without water, and supplies to some areas were not expected to be restored until April or later. After the 2011 Great East Japan Earthquake and tsunami, too, 2.57 million households in 19 prefectures were without water. Access to this vital resource after earthquakes is a major issue.
It is one that threatens Tokyo as well. The government-led Headquarters for Earthquake Research Promotion says there is a 70% chance of a magnitude 7 quake centered in Tokyo occurring in the next 30 years. The Great Kantō earthquake of 1923 had an estimated magnitude of 7.9, suggesting that there is a real possibility of greater Tokyo being hit once again by an earthquake of similar magnitude.
Would Tokyo’s waterworks withstand an earthquake centered on the capital? Research into the answer to this question turns up some worrying information. According to a report on seismic retrofitting of the water network published by the Ministry of Health, Labor, and Welfare in March 2024 and covering fiscal 2022, only 13.2% of Tokyo’s water treatment facilities have undergone seismic upgrades. In fact, Tokyo fares worst of any prefecture, with a score that falls far below the national average of 43.4%. Surely this is an unacceptable state of affairs for what is by far the most populous prefecture.
The water treatment facilities operated by the Tokyo Metropolitan Government’s Waterworks Bureau, which is responsible for the water supply, are larger than those serving other prefectures. This is particularly true with regard to the four facilities fed by the Tonegawa and Arakawa, among some of the largest rivers in Japan.
The metropolitan government assumes daily average water consumption of 4.4 million m³, showing the importance of these four plants, each of which is able to process over 1 million m³ per day. In the Master Plan for Construction of Tokyo Waterworks Facilities and the Tokyo Waterworks Management Plan 2021, both formulated by the Waterworks Bureau in 2021, the government says that it is conducting seismic retrofits of these four plants. In other words, the plants are not currently sufficiently earthquake-proof. Some startling information comes from a former senior Tokyo government official who used to work in the Waterworks Bureau and knows much about the workings of these treatment plants.
“Multiple parts of these four treatment plants are gravely lacking in seismic resilience. Around 80 percent of the water supplied to Tokyo is diverted from the Tonegawa and Arakawa systems that flow north of the capital, and the sheer size of these four treatment facilities means that they form a pivotal role in Tokyo’s water system. If a magnitude 7 earthquake were to hit greater Tokyo, damaging these plants so significantly as to put them out of operation, the supply of water to Tokyo residents would be severely affected.”
Vulnerabilities Shock Even Insiders
The Waterworks Bureau has thus far commissioned private contractors to perform several seismic assessments of treatment facilities, including one after the 2011 Tōhoku quake. These assessments determine the extent to which the various components of the water treatment system would be able to withstand an earthquake, based on a simulation using a waveform derived from a “level 2 seismic vibration”—the largest considered to be possible in the area. The former official says the findings were only shared with the bureau’s construction division, which commissioned the report, and could not be accessed by any of the other divisions. His suspicions aroused, he used his connections to obtain the report through an unofficial route. What he saw caused him to gasp.
“I was like, ‘this is bad.’ I could feel the blood draining from my face. I believe the bureau classified the report as confidential because the results were far worse than even they expected, and they felt that that it couldn’t be allowed to get out. That’s how shocking it was.” Most treatment plants comprise multiple treatment systems, each with settling and filtration ponds, he notes. The settling ponds use chemicals to coagulate suspended matter, causing it to settle so it can be removed. Next are the filtration ponds, which purify the water by passing it through layers of sand and gravel. “This means that even should part of the plant be shut down due to a malfunction, the remaining systems can process more water so that the plant continues to operate. There are, however, a few what could be described as bottlenecks—areas with less redundancy—the failure of which would shut down the entire plant. A considerable number of these bottlenecks were rated very poorly for seismic resistance,” he says.
Seismic Resilience Less than a Third of Required Levels
According to this official, seismic deficiencies were observed at “bottlenecks” in the Asaka, Kanamachi, and Misato plants. For example, take the river pump station located underneath the Asaka treatment plant, Tokyo’s largest, which pumps river water to the surface. The most important part of the system, this station pumps water from a diversion weir on the Arakawa, through an inlet channel 30 meters underground, then back up to the plant. It also pumps water to the Higashimurayama treatment station.
“Multiple locations under the pumping station do not meet seismic requirements,” explains the official. “The underground channel that carries water from the river scored especially poorly. If this is damaged by a magnitude 7 earthquake, we’ll be unable to pump river water to the treatment stage or to the Higashimurayama treatment station. This would drastically cut the volume of water supplied to Tokyo.”
Some elements of the Asaka plant pumping station have less than one third of the required seismic resistance. One is forced to conclude that the former official’s fears could very much come true.
Both the Kanamachi and Misato treatment plants also harbor serious defects. The Kanamachi plant has two intake towers that draw water from the river. Constructed in 1941 and 1964, seismic evaluation found several issues with these historic structures . As is the case with the Asaka pump station, if these towers sustain damage, the facility will become unable to capture river water. Settling ponds, filtration ponds, and many other elements of the facility also did not meet seismic requirements, and, like the towers, are identified as requiring seismic reinforcement work.
An intake tower at the Kanamachi treatment plant. (© Power News)
At the Misato plant, too, the pump station, as well as sedimentation ponds and other elements of the system, scored poorly for seismic resilience. According to the former metropolitan official, while no seismic evaluation was performed of the inlet channel or the junctions that connecting the outlet reservoir and the pipes leading to the pump well, the design of the system means that many points would be unable to withstand major tremors, making it likely that water would leak due to elements being pushed out of alignment or becoming detached. After the 2011 disaster, an aftershock registering local seismic intensity of 5 caused inlet channel junctions at the Misato plant to leak significantly, requiring the flow of water through the channel to be shut down before the plant could be restarted.
Multiple Outages Could Create Water Refugees
As discussed, all of the treatment stations present risks. The worst case scenario is one in which two or more of these facilities become unusable simultaneously. The former official explains:
“If only one of the four treatment stations fails, the supply reservoir will switch to a backup supply from another plant. This might result in a loss of service or a reduction of pressure in some parts of Tokyo, but at worst, we should be able to overcome it with water tankers. However, if two or more of the four treatment plants fail simultaneously, that is a different story. The sheer size of the plants means that they will take a long time to get back online. Even if, as was the case with the recent Noto earthquake, other local bodies send water trucks and other assistance, it will be extremely difficult to supply water to Tokyo on a continuous basis because of its much larger population. Tokyoites will be forced to flee to other, less affected, areas to get water. The question is whether Tokyo’s neighbors have the capacity to take in what could be millions of refugees in such a devastating situation.”
There are still emergency measures that can be taken immediately after an earthquake. Tokyo is home to 213 emergency storage tanks, situated such that most residents have one within 2 kilometers of their homes. These underground tanks are filled with drinking water, enough to supply the daily adult requirement of 3 liters to everyone who takes a container to fill up after an emergency. Note that the 3-liter figure only covers drinking water, and does not include water for washing or flushing toilets. These underground tanks store the equivalent of three weeks’ worth of water for Tokyo’s 14 million inhabitants. However, according to the former Waterworks Bureau employee, some of that water might be used to fight fires that break out after the earthquake, and more may be lost to leaks. It is therefore unclear whether there would actually be enough water for the assumed period. Should it take longer than three weeks for treatment facilities to be come back on line, Tokyo’s residents will be very thirsty. And if neighboring prefectures are not able to accept displaced persons fast enough, it could result in an unprecedented situation in the form of a large number of “water refugees” with nowhere to go.
Report Avoids Inconvenient Truths
Delays to the resumption of water services are something that could really happen. After the Noto earthquake, damage to treatment facilities and water mains caused many areas to be without water, and even temporary water services remained unavailable in some parts of the Ishikawa municipalities Suzu and Nanao for up to three months. According to modelling of an earthquake centered on Tokyo released by the Tokyo Disaster Prevention Conference in May 2022, the restoration of water services after the rupturing of watermains after an earthquake centered in the southern part of central Tokyo is estimated to take around 17 days. However, this simulation assumes that damage will only extend to the network of water mains that crisscross subterranean Tokyo, and does not take into account any damage to treatment facilities.
On the eventuality that treatment facilities could sustain damage, the 2022 report only states, “We should bear in mind the possibility that the extent of damage could be much greater, causing a prolonged delay before services are restored,” and fails to say just how long this would be. Just how long is a prolonged delay? The former official makes the following prediction:
“To use the Asaka treatment plant as an example, if water stops flowing through the inlet channel, which is thirty meters underground, major excavation work may be required. And damage caused by the earthquake isn’t likely to be limited to water infrastructure, meaning it will be difficult to secure workers or materials. This is true of the other parts of these large treatment facilities, too—they could take months or even years to go back online. It appears that the metropolitan government decided if they were truthful about the facts, it would be too much of a shock for Tokyo’s residents, which is why the official report avoids the subject.”
Should supplies of water be interrupted to Tokyo’s large population for an extended period, the effects will far eclipse those seen after the Noto earthquake. Some people will be forced to leave their homes to get water, and, as the former official says, it is doubtful that neighboring areas will be able to receive so many refugees. Tokyo is also home to the head offices of many corporations. Should it become uninhabitable for an extended period, both the Japanese and global economy will also suffer considerably. Overwhelmed by the disaster, it is also possible that the Diet, and the government and its ministries, could also cease to function.
(Originally published in Japanese. Reporting and text by Power News. Banner photo: The Kanamachi water treatment plant from the air. © Jiji.)