Mino Water Purification Plant

What Is the Mino Water Purification Plant?

The Mino Water Purification Plant (三野浄水場, Mino Jōsuijō) in Mino 1-chome, Kita-ku, Okayama City, is the treatment works of Okayama's municipal water system, which began supplying water in 1905, and three of its original structures were registered as Registered Tangible Cultural Properties on February 9, 2005.

The three are the No. 1 Water Source Intake on the Asahi River, the slow sand filter beds, and the former power room and water transmission pump room. Together they trace the route water still takes today: drawn from the river, filtered slowly through sand, then pumped up to service reservoirs on Handayama hill to the northwest for distribution across the city.

The Okayama City Waterworks Bureau points out that most of the system's opening-day facilities survive and that many are still in use. Walking the Mino site, you can follow more than a century of waterworks engineering, from intake to pumping, without leaving one property.

Japan's Eighth Modern Waterworks

Okayama grew up on the alluvial plain of the Asahi River, where well water was poor and cholera outbreaks were frequent. In 1890 the city invited the British engineer W. K. Burton to survey and design a water supply, but his scheme cost several times the city's entire annual budget, and floods in the following years pushed it aside.

Cholera returned in the mid-1890s. In 1897 Mayor Oda Yasumasa pressed the case for a waterworks and commissioned the engineer Yoshimura Chōsaku, who had been building the water supply for the army's Fifth Division in Hiroshima, to draw up plans. The city council split bitterly between those who wanted to postpone and those who wanted to build now; a severe cholera epidemic in 1902 settled the argument.

Ground was broken at the Mino source site in February 1903. Despite shortages of materials and labor during the Russo-Japanese War, construction was largely finished by March 31, 1905, and the first water flowed at a ceremony held at the Handayama reservoirs on July 23 that year. Okayama thus became the eighth city in Japan with a modern waterworks, after Yokohama, Hakodate, Nagasaki, Osaka, Tokyo, Hiroshima, and Kobe. By the end of fiscal 1905 it served 23,370 people. In 2005, its centenary, the city named July 23 "Okayama City Water Day."

Three expansions followed, in 1912 to 1922, 1924 to 1927, and 1935 to 1937. The second added a new intake and more filter beds; the third came after the Muroto Typhoon flooded Okayama in September 1934 and included diesel generators as standby power.

Layout of the Three Registered Structures

The easiest way to picture the site is to follow the water. The No. 1 Water Source Intake sits on the right bank of the Asahi River at the northeast edge of the plant. According to the Agency for Cultural Affairs, the slow sand filter beds lie about 260 meters west of the intake and receive water from the settling basins. The former power room and pump room stands just north of the filters; its pumps sent filtered water up to Handayama.

The Waterworks Bureau singles out a shared look across Okayama's early water facilities: red brick set against white cut granite, a stone typical of the region. The intake and the filter beds were registered for contributing to the historic landscape of the country, and the pump house as a model of design.

The Mino structures were registered together with six features of the Handayama reservoirs and the Kyobashi water pipe bridge, ten waterworks properties in all. The Handayama reservoirs, which receive water pumped from Mino, sit at about 50 meters above sea level on the hill northwest of the plant.

Visiting: Water Museum, Plant Tours and Access

Mino is a working treatment plant, and most of it lies behind high walls. Individual visitors enter through the Okayama City Water Museum (岡山市水道記念館), which occupies the former power room and pump room inside the plant grounds. It opens from 10:00 a.m. to 4:30 p.m. (last entry 4:00 p.m.), admission is free, and it closes on Mondays (or the following day when Monday is a public holiday) and over the New Year period (December 29 to January 3; December 28 to January 4 for the 2026 season).

To see the settling basins and filter beds inside the fence, you need to join one of the Waterworks Bureau's plant tours. These are for groups of roughly ten or more, run Tuesday to Friday except public holidays and the New Year period, and take about 90 minutes: a video and briefing, a walk through the plant, then time in the Water Museum. The bureau asks groups to telephone the Water Purification Division (086-222-3939) to check availability before sending an application. Guidance is in Japanese.

The plant grounds are non-smoking, and food is not allowed (drinks may be taken outside the museum). Pets are not permitted, though assistance dogs are welcome. The bureau's visitor notes say nothing about photography, so follow staff instructions on site.

A construction project to replace the plant's clear-water reservoir and pump building is scheduled to run from October 2024 to March 2030, with work generally on weekdays between 8:00 a.m. and 5:00 p.m. Expect construction vehicles at the gate.

The nearest station is Hōkaiin (法界院) on the JR Tsuyama Line, about a 10-minute walk away. From the Okayama Station area, Okaden and Uno buses stop at Suigenchi (水源池), about two minutes on foot from the plant. Drivers can reach it in around 20 minutes from Okayama Interchange on the Sanyo Expressway; there is space for about 15 cars inside the grounds.