Sue Water Purification Plant No. 6 Slow Sand Filter

The North-West Corner

The Sue Water Purification Plant No. 6 Slow Sand Filter (末浄水場六号緩速ろ過池, Sue Jōsuijō Rokugō Kansoku Rokachi) is a reinforced concrete filter bed built in 1931 at the Sue Water Purification Plant in Suemachi, Kanazawa City, Ishikawa Prefecture, and was registered as a national Registered Tangible Cultural Property on 28 August 2001. It lies west of the No. 4 filter, at the north-west corner of the whole filter field. It covers 1,375 square metres and has its own clear-water well to collect the filtered water.

The Sue Water Purification Plant No. 6 Slow Sand Filter is the last of the six, with the collecting well and pump room just to the west. Slow sand filtration passes water gently down through a bed of sand. A living film forms on the surface of the sand and does much of the cleaning, so the method relies little on chemicals but needs a great deal of space. At Sue the answer was six filters, three on each side of the walkway that carries the supply axis west.

The Kanazawa City Public Enterprise Bureau dates the completion of all six slow sand filters to June 1931 and gives each clear-water well an area of 14 square metres. The original filters still carry the slow-filtration line today.

Where the Six Streams Meet

The filter was registered for its contribution to the historic landscape. In its entry for the Sue Water Purification Plant No. 6 Slow Sand Filter, the Agency for Cultural Affairs sums up the layout of the whole filter field and where the water goes.

Filtered water from every bed joins a collecting pipe laid beneath the east-west walkway. Output from the six clear-water wells merges into that single line and enters the collecting well at the end of the walkway. This filter is the last point at which water joins.

The Agency also notes that the six wells, set three by three in mirror image along the walkway, are small but sit easily in their setting and are widely liked by local people. It is the row of little well houses, rather than the filters themselves, that has become the public face of the place.

The supply axis from the garden pavilion to the collecting well is described by the Agency as the backbone of the plant's plan. No. 6, near its western end, completes the symmetry.

Seeing It

The Sue Water Purification Plant No. 6 Slow Sand Filter can be seen up close only on the plant's pre-booked group tours, which the bureau says cover the sedimentation basins and filters and last about 40 minutes. Tours are for groups such as local governments and community associations, and applications are due two weeks ahead.

The filter field lies well west of the front garden and cannot be approached from the area open without booking. Near the western end of the walkway, turn and look back east to take in the three-and-three symmetry of the well houses.

Nothing is published on photography, so ask the guide. Directions and garden hours are on the Sue Water Purification Plant page.