Hirase Water Purification Plant

A City Waterworks Opened in 1913

Hirase Water Purification Plant (平瀬浄水場, Hirase Jōsuijō) is the Kofu City water treatment works in Hirasecho, Kofu, Yamanashi Prefecture; construction began in 1909, the plant started supplying water in 1913, and six of its early structures, including a 1935 office building, were entered on the national register of Registered Tangible Cultural Properties between 1997 and 1999.

The plant lies about 8.5 kilometres northwest of Kofu Station, at an elevation of 399 metres where the valley floor meets the hills. Its water comes from the Arakawa River, which rises on Mount Kokushi (2,592 metres). Kofu switched on its piped supply in January 1913, and the city's waterworks bureau counts it as the 26th modern waterworks in Japan. Before that, the old castle town had relied on the Kōfu Jōsui, an Edo-period system that distributed water through wooden conduits.

The Hirase Water Purification Plant has worked on the same site ever since. A second source, the Showa plant, was added in 1958, and the Arakawa Dam was completed upstream in 1986. Today the treatment lines are automated and rated at 126,400 cubic metres a day, the largest capacity of any plant in Yamanashi. The site covers 62,581 square metres.

What makes Hirase unusual is what the engineers chose not to demolish. As tanks and filters were replaced, the stone portals and small well houses that marked key points on the water's route were left standing, including a gate on an intake line that no longer carries any water.

Six Structures Along the Path of the Water

The six registered structures are strung along the route that water takes from the river, through the plant and out toward the city. Followed from upstream, they run in this order:

• No. 2 Tunnel Upper Portal: the entrance to the tunnel that carried river water to the plant, registered in 1999
• Former Intake Gate: the stone portal where that same conduit emerged inside the plant, registered in 1998
• Former Filter Bed Regulating Well: a small round well house that controlled flow and filtration speed, registered in 1997
• Former Katayama Tunnel Upper Portal: the plant-side mouth of the tunnel that sent treated water to the city, registered in 1998
• Former Katayama Tunnel Lower Portal: the city-side mouth of the same tunnel, in Haguro-cho, registered in 1998
• Hirase Water Source Former Office (Suikoan): the plant office built in 1935, now a waterworks museum, registered in 1997

Three of them, the intake gate, the regulating well and Suikōan, stand inside the plant grounds at 437-3 Hirasecho. The No. 2 Tunnel portal and the upper Katayama portal lie elsewhere in Hirasecho, and the lower Katayama portal is at 1715 Nashinoki in Haguro-cho, well away from the plant.

The two tunnels face in opposite directions. No. 2 Tunnel brought raw water in; the Katayama Tunnel sent clean water out. Both ends of the process survive in the same form, as masonry tunnel mouths, which is why the six sites read best as one system rather than as separate monuments.

Registered as Modern Heritage

Registration came in five rounds, beginning with the regulating well in July 1997 and ending with the No. 2 Tunnel portal in August 1999. That was only a year or two after Japan created the registration system in 1996, and the regulating well carries Yamanashi's early registration number 19-0012. The waterworks bureau's list cites the prefecture's survey of modern industrial heritage for all six.

The criteria differ. The Former Intake Gate alone was registered as a structure that has become a model of design, while the other five were registered for their contribution to the historic landscape. The quality of its stone portal, in other words, was judged on its own merits.

In June 2020 all six became component properties of the Japan Heritage story known in Japanese as Kōshū no Takumi no Genryū: Mitake Shōsenkyō, which links the Shōsenkyō gorge upstream with the craft and engineering it supported.

Visiting and Getting There

The Hirase Water Purification Plant is a working utility, and visitors cannot walk in freely. The Kofu City Waterworks and Sewerage Bureau runs guided tours for groups such as school classes and neighbourhood associations on weekdays, excluding public holidays and the New Year break. Morning tours run 9:30 a.m. until noon and afternoon tours 1:00 p.m. until 4:00 p.m.; a visit takes about 1 hour 30 minutes, and groups of up to about 120 people can be accommodated.

Bookings start with a phone call to agree a date, followed by an application form sent by fax. The contact is the bureau's Water Purification Division, facilities section (tel. 055-251-8111), which takes calls on weekdays 9:00 a.m. until noon and 1:00 p.m. until 5:00 p.m. The published guidance says nothing about individual visitors, so anyone travelling alone should ask the same office.

According to the bureau's tour map, groups gather at the clear-water reservoir and follow the treatment process through the receiving well, mixing basin, flocculation and sedimentation basins and rapid sand filters. The river intake and grit basin are outside the tour area. A bureau notice dated June 2023 states that the interiors of the main administration building and the Suikōan museum cannot be visited. The guidance does not mention photography, so confirm it when booking.

By car, the plant is about 8.5 kilometres northwest of Kofu Station on local roads. No public-access arrangements have been announced for the three tunnel portals outside the grounds.