Sue Water Purification Plant No. 3 Slow Sand Filter

Between Two Walkways

The Sue Water Purification Plant No. 3 Slow Sand Filter (末浄水場三号緩速ろ過池, Sue Jōsuijō Sangō 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. 1 filter, in the middle of the south row. It covers 1,375 square metres and has its own clear-water well to collect the filtered water.

The Sue Water Purification Plant No. 3 Slow Sand Filter has No. 1 on one side and No. 5 on the other. 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.

Walkways, Overflows and a Granite Rim

Registered for its contribution to the historic landscape, the Sue Water Purification Plant No. 3 Slow Sand Filter is described by the Agency for Cultural Affairs in terms of the walkways between the filters and the finish of its well.

The filters are separated by service walkways that double as partition walls. Walking on top of the dividing wall combined the route for inspection and sand maintenance with the division between beds. This filter has such a walkway on either side.

At each end of the walkway side a pipe is set to carry off overflow. The rate of slow filtration changes with the condition of the sand, and water levels rise and fall with it, so provision for overflow belongs naturally to the method.

The clear-water well is a concrete tank with a coping of granite and a lid of checker-plate steel. A pale band of stone rims the grey concrete, and the ribbed steel closes it over. Materials chosen for wear and grip end up as a small piece of design.

Seeing It

The Sue Water Purification Plant No. 3 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, look at the granite coping and the checker-plate lid of the well.

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