Sue Water Purification Plant No. 1 Slow Sand Filter

First in Line

The Sue Water Purification Plant No. 1 Slow Sand Filter (末浄水場一号緩速ろ過池, Sue Jōsuijō Ichigō 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 sits at the south-east corner of the filter field, on the south side of the walkway. It covers 1,375 square metres and has its own clear-water well to collect the filtered water.

Water drawn from the western end of the sedimentation basins is distributed to six filters on lower ground. The Sue Water Purification Plant No. 1 Slow Sand Filter takes the south-east corner, at the head of the row. 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.

The Wall and the Well

Registered for its contribution to the historic landscape, the filter is one of six laid out in mirror image along the walkway, a plan made together with the front garden.

The Agency for Cultural Affairs describes the Sue Water Purification Plant No. 1 Slow Sand Filter, like the others, as enclosed by reinforced concrete walls rising almost vertically. The sedimentation basins have raked lower walls; the filters do not. Straight walls make it easier to lay a flat bed of gravel and sand.

On the north side, facing the walkway, is a concrete clear-water well. Water that has passed through the sand is gathered at the bottom of the bed, collects here, and runs west through a pipe under the walkway to the collecting well. Six filter-and-well pairs face the walkway in the same way.

The Agency describes a different feature for each of the six: siting and walls for No. 1, the filter bed for No. 2, walkways and well for No. 3, the well houses for Nos. 4 and 5, and the overall arrangement for No. 6. No. 1 is the introduction.

Seeing It

The Sue Water Purification Plant No. 1 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. On a tour, note how steeply the walls rise and where the well sits against the walkway.

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