Four hundred years ago, this body of water extended almost to the main gate of Edo Castle. It was a shallow sea called Hibiya Inlet. In the low-lying land created by reclaiming the sea, digging wells yielded only salty water.

⏱️ Table of Contents
0:00 The Sea in Front of Edo Castle | Hibiya Inlet and Salty Well Water
0:48 Spring Water of Inokashira Pond | Bringing Water from the Musashino Plateau to Edo
1:28 Kanda Aqueduct and Suidobashi | Edo's First Full-Scale Water Supply System
2:24 Hamura Intake Weir | Bringing Water from the Tama River to Edo, 40km Away
3:04 Tamagawa Aqueduct 43km | Completed in 8 Months Without Heavy Machinery
4:00 Yotsuya Okido | In 1654, Water from the Tama River Reached Edo
4:32 Edo's Wells Were Water Tanks | Underground Stone Pipes, Wooden Pipes, and Buried Manholes
5:28 Nobitome Aqueduct and Water Distribution | Villages and Fields Developed on the Musashino Plateau
6:08 Sekiguchi Oarai Weir | A Weir Depicted in the Edo Meisho Zue (Illustrated Guide to Famous Places of Edo) for Drinking Water
6:40 Cholera and the Improved Water Supply | Wooden Pipes Replaced with Iron Pipes at Yodobashi Water Treatment Plant
7:36 Hamura's Towatari Weir | Log Weir Turns into Concrete
8:08 The Tamagawa Aqueduct Today | A National Historic Site, 12km Still in Use

The town continued to expand. However, as it expanded, the amount of drinkable water available to the residents decreased. So, they reversed their approach, stopping the search for nearby sources and deciding to go for the water itself, 40 kilometers west, to the Tama River.

The Tamagawa Aqueduct is 43 kilometers long. The elevation difference between the starting and ending points is only 92 meters, and the water only drops 21 centimeters for every 100 meters traveled. This is close to the limit of how much water can flow. Even one measurement error would stop the water flow. Yet, they dug it in eight months using only hoes and baskets.

Beyond Yotsuya Okido, the water never reappears above ground. From stone conduits to wooden conduits, from wooden conduits to buried manholes, and from buried manholes to wells. Edo's wells weren't simply dug holes, but rather reservoirs with wooden pipes connected to the bottom. Even though digging yielded no water, pulling up a bucket revealed water. The Kanda and Tamagawa aqueducts operated on this system for 250 years.

*The video and audio in this video were generated by AI.

[Stories not included in the video]
■ The limit of the slope — 21 centimeters for every 100 meters traveled. Even after traveling 43 kilometers, it only descended 92 meters. Even as the terrain changed from forest to plains and then to fields for 12 kilometers upstream, 18 kilometers midstream, and 13 kilometers downstream, this slope remained constant.

■ Where the water disappeared — In Hino, it is said that the water flowed was absorbed into the sand and disappeared. This layer was called "water-eating soil."

■ How eight months were counted — Eight months from the start of construction to the opening. This year had an intercalary sixth month, hence the counting.

■ Thirty-three water diversions — During the Kansei era, there were thirty-three water diversions between Hamura and Yotsuya. This accounted for approximately half of the water taken from Hamura. The largest diversion was the Nobitome Canal, which extended for several kilometers to dry plateaus that previously lacked water. The water supply system even changed the landscape outside of Edo.

■ Dimensions of the wooden pipes — The planks were approximately eight centimeters thick. They were assembled into square pipes using boat nails, and the joints were filled with cypress bark to stop the water. At the points where the pipes converged, buried manholes approximately 1.3 meters on each side and 1.6 meters high were installed.

■ Drinking water becomes a famous spot — The Sekiguchi-Ōarai Weir was a famous Edo landmark where water fell in a single, continuous stream. It was depicted in the Edo Meisho Zue (Illustrated Guide to Famous Places of Edo), and there were even teahouses on the banks overlooking the weir.

■ Cholera and Wooden Pipes — Cholera entered Edo in 1858, and outbreaks occurred almost every year thereafter. The major outbreak in 1886 resulted in approximately 10,000 deaths. Underground, the wooden pipes rotted, and soil mixed in through the joints.

■ From Wood to Iron — Construction began in 1893, and water flow started in December 1898. The planned capacity was 170,000 cubic meters per day, reaching 240,000 upon completion. The wooden pipes, which had been in use for 250 years, were replaced with iron pipes. In June 1901, the Kanda and Tamagawa aqueducts ceased supplying water to the city.

■ The Day Water Returned — In 1965, the Yodobashi Water Treatment Plant was abolished, the filtration ponds were filled in, and high-rise buildings were constructed on the site. Water returned to the dry moat in August 1986. However, it was not water from the ...