For centuries, the boastful citizens of Edo lorded it over country bumpkins by saying, “I’m an Edokko [native of Edo] ’cause I was cleaned with pipe water when I was born and I’ve grown up drinking pipe water ever since.”

It seems an odd thing to crow about given the cultural wealth of Edo, at the time the largest city in the world, but this pride in the city’s water system wasn’t misplaced. Cool, pure water carried by pipes to the city’s remotest corners was indeed a byword for the quality of life in Edo — as well as being the lifeblood of the city’s prosperity.

However, coming up with an efficient and reliable water supply was no easy task. Much of Edo was built on land reclaimed from the shallow waters of Edo Bay, which — in the absence of the technology required to bore deep wells — only yielded brackish water. Meanwhile, Edo Castle and the samurai residences were mostly situated on uplands on the eastern edge of the Musashino Plateau. There, potable water was equally hard to come by because the friable top soil was not water-retentive. Indeed, the vast grasslands of Musashino had traditionally been ridiculed by Kyoto aristocrats, who lamented in poems that “Musashino has neither trees nor mountains behind which the moon can set.”

But when Ieyasu chose Edo as the administrative center of his new fiefdom centered on the Kanto Plain, he was, of course, well aware of the water issue. In fact, on July 12, 1590, prior to his arrival at Edo on August 1, he dispatched his trusted retainer Okubo Togoro to investigate the local water supply.

Okubo dug a waterway in Edo from Koishikawa (in present-day Bunkyo Ward) to satisfy the needs of the burgeoning new town growing up around Nihonbashi. By 1629, this rudimentary supply line had been expanded into the Kanda Canal, which channeled supplies from Inokashira Pond in present-day Mitaka into the Kanda River, then into a canal cut through the surrounding hillsides. After filling the ponds and streams in the elegant Korakuen Garden created by Lord Tokugawa of Mito, the canal water then entered the heart of the city along a wooden aqueduct across the Kanda River. Altogether, this system served the eastern sections of Edo, supplying about 25 percent of the total demand.

Being at first sparsely populated, the city’s southwestern sections were sufficiently supplied with water from Tameike Pond. In the course of the city’s expansion, however, the pond kept shrinking until it was eventually incorporated into the outer moats of Edo Castle. It now survives only as the name of a subway station, Tameike-Sanno.

However, as the population kept doubling and redoubling from about 200,000 in 1610 to more than 400,000 by 1640 and then to over a million — even possibly up to 1 1/2 million by the mid-18th century, had censuses included the daimyo households and samurai classes — the city was in need of a much larger water source. The answer was to be found in the Tama River, to the northwest of the city, where the senior shogunal official Lord Matsudaira Nobutsuna (1596-1662) commissioned two commoner brothers, Shoemon and Seiemon, to construct a system to carry the river’s water to Yotsuya, on the city’s northwestern perimeter.

The brothers accomplished the task despite great hardships. In the new system, completed in 1653 and named the Tamagawa Canal, water was diverted from the river by a dam in the village of Hamura, from where it was channeled 43 km along an open canal to Yotsuya. From Yotsuya, water was guided into stone, wooden and bamboo pipes that crisscrossed the city underground. However, as the entire water flow depended on the force of gravity, the canal had to be precisely planned to slope only very gradually so that its Yotsuya outlet was high enough to allow water to flow out and down to every nook and cranny of the city.

This water not only quenched citizens’ thirst, but also fed the trees and flowers that were planted all over, both in the samurai gardens and in poor commoners’ pots on sidewalks. Indeed, the abundance of trees and highly developed horticulture for which Edo was so admired by visiting Europeans in the 1850s and ’60s would have been notably absent without that water supply.

However, the Tamagawa Canal also transformed Edo’s arid suburbs into fertile villages. A typical example is Nobidome in southern Saitama Prefecture. The notoriously dry grassland there (as nobi, meaning “wild fire,” implies) was part of the fiefdom of Lord Matsudaira, who was granted permission by the shogun to divert 30 percent of the canal’s water. Although the 25-km Nobidome Canal along which he channelled it took only 40 days to dig, it took three years to fill because the parched soil at first just soaked up water like a sponge.

When he died, Lord Matsudaira was buried at Heirin-ji, the Matsudaira family temple that was moved to Nobidome. Nowadays, the large compound of the Zen temple is a verdant woodland designated as a natural monument — thanks to successful irrigation 350 years ago.

Though continually tapped in modern times, the Tamagawa Canal finally went out of use in 1965 when it was replaced by the new Tone River system. Thereafter, the historic canal was abandoned by the authorities, except for its upper stretch in Hamura. Dried up and fast decaying, it then seemed fated to become yet another culvert in the Tokyo sprawl. Citizens, though, had not forgotten the fond memory of a rushing stream that once flowed fast past green banks. In 1986 local residents’ passionate, persistent calls for the preservation of Tamagawa Canal were finally answered when water was returned to the empty canal — albeit water recycled from a nearby treatment plant. With the return of the water, trees were resuscitated and birds and dragonflies returned to the 30-km stretch of the waterway that has evaded developers so far.

Finally, on May 16 this year, the Tamagawa Canal won national designation as a historic site — a metropolitan designation it was accorded in 1999.

What was for so long essential to life in the city is now a welcome strip of green, a linear oasis in a concrete wasteland.

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