Tachikawa Water History: Where the Tap Water Comes From, and Wells

Where Tachikawa’s tap water comes from: distant rivers, 24 deep wells beneath the city, the 1952 wells that smelled of petrol, and water for disaster days.

日本語で読む（Japanese version）

Turn on a tap in Tachikawa and water comes out. Nothing could be more ordinary. But I had never once wondered where that water came from.

I vaguely assumed it was Tama River water. Tachikawa (立川) is a town on the banks of the Tama River, in the Tama area — the western half of Tokyo beyond the 23 central wards. Yet the documents of the Tokyo Metropolitan Government Bureau of Waterworks say that 80 per cent of Tokyo’s water comes from the Tone and Arakawa river systems. Water from the direction of Gunma and Saitama, far to the north, may be reaching kitchens in Tachikawa.

And there was something else. In the list in Tokyo’s annual water-quality report were more than twenty wells for the public water supply, bearing the names of Tachikawa’s neighbourhoods: Shibasaki, Fujimi, Sunagawa, Sakaecho, Nishisuna. Water is being drawn up from far, far below our feet.

As I read on, I came across an even more surprising record. In 1952, Tachikawa’s well water was so dirty that questions were asked about it in the national parliament, the Diet. The wells, it was said, smelled of petrol.

Where does Tachikawa’s water come from, and what path has it taken? Let me travel back up the pipe, to the other side of the tap.

Where does Tachikawa’s tap water come from? The Tone, the Tama, and the wells underfoot

Let me start with Tokyo as a whole.

According to the Bureau of Waterworks, almost all of Tokyo’s water sources are rivers: 80 per cent from the Tone and Arakawa river systems, and 17 per cent from the Tama River system. The water rights Tokyo holds amount to about 6.8 million cubic metres a day. Until around 1960, most of the water came from the Tama River system, but as demand rose sharply after that, Tokyo came to depend more and more on the Tone.

You live in a Tama River town, yet much of what you drink may come from the Tone. It gives you the odd feeling of having let down your own local river.

What about Tachikawa? Water supply in the Tama area works a little differently from the 23 wards. According to the Bureau of Waterworks’ Tama-area water-quality report for fiscal 2020, the 26 cities and towns of Tama and Tama New Town had about 3.96 million people on the supply, with an average of about 1.17 million cubic metres a day distributed. About 89 per cent of that was sent in as “supplementary water” from the Higashimurayama and Ozaku purification plants and others. The remaining 11 per cent or so, called “district water”, is river water, riverbed seepage and groundwater drawn within Tama itself, treated or chlorinated and distributed locally. And about 83 per cent of that district water is groundwater pumped from public-supply wells.

So what reaches a tap in Tama may be a mix of water from distant rivers and water from the wells beneath your feet. The report says few areas receive district water alone; most facilities take in supplementary water from Higashimurayama and elsewhere and distribute it mixed with district water.

Tachikawa’s water routes can be traced in the system diagram in the fiscal 2023 report. Tachikawa’s Shibasaki water supply station sits on the Higashimurayama plant’s system, and the Tachikawa Sunagawa supply station on the systems of the Ozaku and Higashimurayama plants. The Fujimi No. 3 purification station and the Tachikawa Sakaecho purification station are each drawn as systems in their own name.

Where does the Higashimurayama plant take its water from? According to Wikipedia, the online encyclopedia, its four main sources are Lake Tama, Lake Sayama, the Tamagawa Aqueduct, and the Akigase intake weir on the Arakawa. The Bureau of Waterworks explains that the Asaka plant, which takes Tone water from the Arakawa, and the Higashimurayama plant, which takes Tama River water via the Hamura intake weir and the Murayama and Yamaguchi reservoirs, are linked by a “raw water connecting pipe” about 17 kilometres long and 2.2 metres across, so they can pass raw water to each other. In normal times they mainly use Tone and Arakawa water, and keep Tama River water — in the Ogochi reservoir and others — in storage as far as possible. In a drought or a water-quality accident, the Tama River water is brought into play.

The Higashimurayama plant’s own history is packed with the history of Tama’s water. According to the encyclopedia, work began in 1932 as the City of Tokyo’s second waterworks expansion, together with the Ogochi reservoir, and after an interruption for the war it began supplying water on 16 August 1960. At first its raw water came from the Tama River system alone, but Arakawa water was connected in 1964 and the Tone system in 1965. 1964 was the year of the Tokyo Olympics, and the encyclopedia’s entry for the Ozaku plant also mentions the great Tokyo drought of that same year. Just when the Tama River alone could no longer quench Tokyo, Higashimurayama joined hands with the Tone. Today it is one of Tokyo’s four great purification plants, handling 18.4 per cent of the total. Because it stands on relatively high ground, the encyclopedia adds, it sends water to the central wards by gravity. From the plant looking out on the Sayama Hills, the water flows east across Tokyo as if running downhill.

Rain that fell on the mountains of Okutama, and water from the upper Tone. The two are joined by a thick pipe underground, and at a supply station just short of Tachikawa they are sometimes mixed with water from the wells underfoot. A glass of tap water has come from much further away than you would think, by several roads.

The wells sleeping under the city: Shibasaki Nos. 1 to 9

Let us turn to the wells underfoot.

The Bureau of Waterworks’ Tama-area water-quality report for fiscal 2020 includes a list of source wells in Tama. Count the Tachikawa entries and there were 8 treatment facilities and 24 source wells.

At the Shibasaki supply station stand nine wells, Shibasaki No. 1 to Shibasaki No. 9. The same station also has Fujimi Nos. 1, 2, 3 and 6. Fujimi Nos. 4 and 5 are one each at the Fujimi No. 1 and No. 3 purification stations. The Tachikawa Sunagawa supply station has Sunagawa No. 2 and the Kashiwacho well. The Tachikawa Sakaecho purification station has Tachikawa Sakaecho Nos. 1 to 3. The Sunagawa Chubu station has Sunagawa No. 1 and the Kamisuna well. The Nishisuna No. 1 and No. 2 stations have Nishisuna Nos. 1 and 2.

Reading the list, I felt as if I were reading the car numbers on a train platform. Shibasaki is a long train of nine cars, while Fujimi’s cars 4 and 5 have been coupled to other trains. You can sense the meticulous labour of whoever numbered the wells.

What kind of water is it? According to the same report, groundwater in Tama has a pH between 6.9 and 8.4 — weakly alkaline overall. Its hardness, the measure of calcium, magnesium and so on, ranged from 12.0 to 148 milligrams per litre. The top figure is more than ten times the bottom one. Even under the same Tama ground, the character of the water differs a great deal from well to well. The report also notes that the water quality of source wells is tested once every three years.

Groundwater brings new worries, too. The City of Tachikawa has tested for organic fluorine compounds (PFAS) at 9 wells owned by the city and 19 wells owned by businesses and residents in the city, and published the results. For tap water, a water-quality standard for the combined value of PFOS and PFOA came into force on 1 April 2026. Wells silently store up the past and the future of their land.

Speaking of what lies under Tachikawa, there is one more thing I want to mention. It was long said that an active fault named after the city, the “Tachikawa Fault”, ran here. According to the encyclopedia, however, a survey reported in 2015 concluded that the confirmed fault was about 12 kilometres around Hakonegasaki in the town of Mizuho and did not exist within Tachikawa at all; in the report it was renamed the “Hakonegasaki Fault”. The fault that carried Tachikawa’s name was not in Tachikawa. What is definitely at work under Tachikawa is not a fault, but twenty-odd wells.

Water was far away on the plateau: the age of wells and branch channels

Today we can draw water from deep wells, but the old Tachikawa plateau was a place that struggled for water.

The City of Tachikawa explains that many branch channels were drawn from the Tamagawa Aqueduct onto the Musashino Plateau, where the water table was so low that people could not live. The Bureau of Waterworks also writes that because the aqueduct runs along the ridge of the plateau, water could be branched off to every part of it, and the branches served as drinking water, irrigation and power for water-wheels, contributing greatly to the development of the dry Musashino Plateau. Around 1791, 33 branch channels were on record. I walked the aqueduct and the Sunagawa branches in another article in this feature, so here I only want to note that the villages on the plateau survived on the aqueduct’s branches before they survived on wells.

At the southern edge of the plateau, meanwhile, below the bluff near the Tama River, there were springs. As I wrote in the Nekawa article, around Nishiki-cho there was once a place called Idobata — “by the well” — where spring water gushed out in abundance. At the site of Mangan-ji Temple, only the well still remains. On the plateau, water was far away; below the bluff, it was close. Tachikawa’s water map was drawn, from the start, by that difference in height. (On the bluffs and springs, see also our Yagawa and hake article.)

Then, after the war, Tachikawa’s wells came to threaten people’s lives in a way no one could have foreseen.

1952: the wells smelled of petrol — how Tachikawa’s water supply began

The website of the House of Representatives still holds a written question submitted in 1952 and the government’s written answer. Its title: “Question concerning the pollution of drinking water in Tachikawa City.”

The answer, dated 13 June that year, says this. Bad smells and pollution were found in some of the well water in Tachikawa from around 1948; from around 1951 it became especially bad in parts of the area around the airfield used by the US forces stationed there, and spread. It affected 1,600 households, about 10,000 people. Water from wells 30 to 40 shaku deep smelled of petrol and contained oils; some was cloudy and rust-coloured, and it was unfit to drink.

Thirty to forty shaku is roughly 9 to 12 metres. Wells of a depth dug by hand, and drawn with a bucket on a rope or a hand pump, were giving off the smell of petrol.

In November the same year, another member of the Diet submitted a written question. It said the pollution had spread across Fujimi-cho, Akebono-cho, Shibasaki-cho, Nishiki-cho and Takamatsu-cho, and that 2,317 households and 9,965 people had no choice but to use this water, directly or indirectly, for drinking. Because supply by water truck was limited to certain hours, it added, people with jobs and others were still obliged to drink the polluted water.

The answer dated 21 November gave the cause: oil had leaked from a damaged point in a pipeline belonging to the US forces stationed near Tachikawa and had seeped gradually into the ground. This had been established by the forces’ own investigation, following talks in the Japan–US Joint Committee. A site inspection on 22 July that year had confirmed the damage was repaired. In the results the metropolitan health bureau chief sent to the mayor, it added, among some 880 tests, none had found lead above the level the state allowed in drinking water.

And there was only one solution, the answer said: lay water mains and start supplying water as quickly as possible.

Here the beginning of Tachikawa’s water supply comes into view. The City of Tachikawa’s chronology records under 1951: “Tachikawa City begins its water supply service.” According to the answer, the city’s original plan was for 23,400 people to be supplied, with an average of 5,400 tonnes a day, 230 litres per person per day, at a cost of ¥187 million. Work had begun in fiscal 1951, but as the polluted area spread, districts outside the plan had to be added. The answer expected supply to begin in part of the affected area by January the following year.

Another answer, dated 10 March 1953, went further. The cause had been thought to be petrol seeping into the ground from the US forces’ base, but recently, it said, suspicion had arisen that petrol was also leaking from underground tanks of the former Imperial Japanese Army. As countermeasures, the authorities had warned the city, the towns and residents, spread knowledge of how to handle “petrol-yielding wells” and how to prevent fires, and where necessary banned the use of well water and designated zones where bonfires and smoking were forbidden. In Tachikawa, water was expected to reach most of the worst-hit areas by the end of March; in neighbouring Showa town, today’s Akishima, emergency water was being supplied with water shared by the US forces.

Do not smoke next to the well. There really was a time when such warnings were issued. I read the answers twice, and then I thought of the tap in my own home.

The April 1959 issue of the medical journal Koshu Eisei (Public Health) also carries a paper by a doctor at the National Tachikawa Hospital, “A study of polluted well water occurring in Tachikawa City”. It opens by noting that the pollution, centred on Tachikawa, reached neighbouring towns and villages as well.

Tachikawa’s water supply was not laid for convenience. It was laid in a hurry, as a replacement for wells that could no longer be drunk.