Thirsty Places: Tokyo

At two in the morning on a residential street in Tokyo, when the traffic has stopped and the city is as quiet as it gets, a man in a waterworks jacket kneels on the pavement and puts the end of a steel rod against a valve cover, and the other end to his ear. He is listening for a hiss. Water escaping from a crack in a main under pressure makes a sound that carries along the pipe, and a trained ear can tell a leak from the noise of a tap running in a house, and tell, within a few metres, where it is. Tokyo's waterworks has been sending people out to listen like this for sixty years, over every kilometre of its twenty seven thousand kilometres of mains, and the result is a number that no other large city has matched: about three percent of the water it puts into the pipes is lost. London loses about a quarter. Most cities on this site lose a third or more.

This article is about where the largest city on Earth gets its water, what the drought of 1964 did to it, how the leaks were found and the pipes replaced, what the waterworks does to make the tap water good enough to sell, and what the cathedral of concrete under the northern suburbs is for.

The rivers

Tokyo sits on the Kanto plain, the largest flat land in Japan, at the mouths of several rivers, and for its first centuries as Edo it drank from them through wooden conduits that were among the longest urban water systems in the world. The modern city drinks from two systems. About four fifths comes from the Tone river and its tributary the Arakawa, which rise in the mountains to the north and are dammed in a chain of reservoirs built after the war, their water carried to the city's treatment works by canal and treated at plants like Kanamachi and Asaka on the city's edge; the Tone is Japan's largest river by basin and the capital region's share of it is fixed by agreement with the farms and the other cities on it. About a fifth comes from the Tama river to the west, dammed in 1957 at Ogouchi to make Lake Okutama in the hills, which was the city's own reservoir and the only one it had when the drought came.

The Olympic drought

The Games of 1964 were the moment postwar Japan showed itself to the world, and in the summer before them the reservoir at Ogouchi ran down toward empty. The rains failed from spring, the Tama fell, and the city, which had grown by millions since the war on a supply built for a smaller one, began cutting: first the pressure, then the hours, then, by August, half the supply to the districts, with tanker trucks in the streets and the newspapers writing about the Tokyo desert. The Games opened in October after the rains returned, and the drought is remembered in the city the way the Day Zero summer is remembered in Cape Town, as the moment the arithmetic was seen. The response was the Tone system: the dams, the canals and the works that moved the city from its own small river onto the largest one on the island, built over the following two decades, so that Tokyo has not rationed since. It was the response of a city that could afford it, and it was only half the response.

Finding the leaks

The other half was the pipes. In the 1950s Tokyo lost about a fifth of its water before it reached a tap, through cast iron mains laid before the war and cracked by the earthquake of 1923, the bombing of 1945 and the ground movement of a city built on soft ground, and in the years after the drought the waterworks decided that the cheapest new water was the water it already had. It replaced the mains, over decades, with ductile iron and steel, with joints designed to flex rather than break in an earthquake, and it replaced the lead service pipes to the houses with stainless steel; it mapped the network, metered every district so that a night flow higher than it should be pointed to a leak, and it built the corps of listeners who walk the streets at night with their rods and, now, with sensors that listen for them. Every leak found is repaired within a day. The rate fell from a fifth to a tenth by the 1970s, to five percent by the 1990s, and to about three percent, which is the figure the leaks article on this site uses as the world's floor. Other cities have the same technology. What Tokyo has is sixty years of spending on a thing nobody sees.

The comparison with London, which this site has made before, is not a comparison of engineers. London's mains are Victorian cast iron in clay that moves with the seasons, and its utility, private since 1989, has spent what its regulator allowed, which has not been enough to replace them; Thames Water loses about a quarter of its water and has been fined for it. Tokyo's utility is public, charges a tariff that covers the work, and has treated leakage as a performance measure for three generations. The water is the same. The pipe is the decision.

Water good enough to sell

The waterworks sells its own tap water in bottles. It began in the 2000s as a way of answering the complaint that Tokyo's water tasted of chlorine and mud, which in the 1980s it did, because the Tone's water comes from a farmed and populated basin and arrives at the works carrying the agriculture and the sewage of the plain above the city. The answer was advanced treatment: every river water works in the city now runs the conventional train the coagulation article on this site describes, and then passes the water through ozone, which the disinfection article covers, and through beds of activated carbon in which bacteria eat what the ozone has broken up, so that the water leaving the works is as clear and tasteless as a mountain spring's and the chlorine needed in the pipes is small. The bottles are a statement rather than a business, handed out at events and sold at the museum, and the statement is that a city of fourteen million drinks a river that runs through farmland and finds nothing to complain of.

The ground that sank

Tokyo also learned, before most cities, what pumping does to the ground. The factories of the eastern wards drew their water from wells through the first half of the twentieth century, and the soft clay under them compacted as the water was taken, so that by the 1960s parts of Koto and Edogawa wards had sunk by more than four metres and lay below the level of the sea and the rivers, behind walls, which the Jakarta and Mexico City articles on this site describe as the condition of those cities now. The prefecture restricted industrial pumping from the 1960s and banned most of it by the 1970s, the water table recovered, and the sinking stopped within a decade, which is the clearest demonstration anywhere that subsidence ends when the pumping does. The zone below sea level remains, a few hundred thousand people behind levees and floodgates in the east of the city, and the drain under the northern suburbs is one of the things that keeps it dry.

The cathedral under the suburbs

The last of Tokyo's water problems is the one the city has too much of. The Kanto plain floods: the typhoons of late summer drop two or three hundred millimetres in a day on a flat land of small rivers between levees, and the northern suburbs, across the border in Saitama prefecture, were built on a floodplain that the rivers took back every few years. The national government's answer, finished in 2006 after thirteen years, is the Metropolitan Area Outer Underground Discharge Channel, the largest storm drain in the world: five shafts, each about seventy metres deep and thirty across, sunk beside five small rivers, joined by a tunnel of six kilometres fifty metres down, leading to a hall of concrete pillars the size of a cathedral and a bank of pumps driven by jet engines that can throw two hundred cubic metres a second into the Edo river. When a river rises, it spills into its shaft; the water runs through the tunnel to the hall; the pumps lift it into the big river, which can take it, and the suburb stays dry. It fills a few times a year, and in the typhoon of October 2019 it took twelve million cubic metres in two days and the floodplain above it did not flood. It belongs to the national ministry rather than to the city's waterworks, and it is the other face of the same habit: the city builds the thing underground that the problem needs, and maintains it.

What it teaches

Tokyo is the city on this site where the water problem was solved by maintenance. The drought of 1964 gave it the dams, which money can build anywhere; what the city did afterward, for sixty years, was replace its pipes and listen for leaks until it lost less water than any city in the world, treat a farmed river until the tap water could be bottled, and dig a drain under the suburbs large enough for the floods the climate sends. None of it is secret and none of it is new. It is public money spent on things underground by a utility that was allowed to spend it, for three generations, and it is the standard against which the leaks, the tankers and the rota days of the other places articles should be read.

Three percent lost, a man with a steel rod at two in the morning, and a cathedral under the suburbs for the water that comes all at once.