An Open Shed for Washing Filter Sand
The Sanjo City Waterworks Bureau Osaki Water Purification Plant Sand Washing Shed (三条市水道局大崎浄水場洗砂場) is a small open-sided shed at the Osaki waterworks in Nakashin, Sanjo City, Niigata Prefecture, where sand from the slow sand filters is washed; it dates from 1933 and was listed as a Registered Tangible Cultural Property on October 28, 2011. It stands just east of the filter beds.
It measures 4.9 meters by 3.8 meters, a building area of 19 square meters, with no walls at all under a gabled sheet-metal roof. The lower part of each column is reinforced concrete; above that, old railway rails are joined in a Y shape to carry a timber roof frame.
The national database dates it to 1933 and also records that it was moved at some point in the mid-Showa period, between 1946 and 1965. Whether it now stands on its original spot is not stated.
What the Old Rails Tell You
The detail to look for at the Sanjo City Waterworks Bureau Osaki Water Purification Plant Sand Washing Shed is the recycled rail. Worn-out railway rails were widely reused as columns for station canopies and warehouses in Japan before and after the war. Here they are forked into a Y, the two arms reaching up to catch the roof frame.
Rail is stiff and strong for its size, so a slender section can hold up a roof. A washing floor needs little more than cover from the rain and columns thin enough to stay out of the way, and salvaged rail fit that brief exactly.
Slow sand filters need their top layer scraped off, washed and put back regularly. According to the Niigata branch of the Japan Society of Civil Engineers, this shed is still used for that work. It was listed as the filters' working partner, modest as it is.
What to Look For
Compare the base and the head of each column. The switch from square concrete stub to slender rail is plain to see, and because the shed is open you can follow how each fork meets the timber above.
The city's reference photograph of the Sanjo City Waterworks Bureau Osaki Water Purification Plant Sand Washing Shed is taken from the west, from the filter side, with the row of columns and the roof square in the frame. Stand at the edge of the beds facing east and you get nearly the same view.
Visiting
The shed is inside the working plant, which is normally closed. When the grounds open in cherry blossom season, look for it east of the slow sand filters. It is a working facility, so stay out and leave the equipment alone.
Directions and opening conditions are collected on the Sanjo City Waterworks Bureau Osaki Water Purification Plant page.
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Q&A
- What is the sand washing shed at the Osaki Water Purification Plant used for?
- It is where sand scraped from the slow sand filters is washed, and it is reported to be still in use for that purpose.
- When was the Osaki plant sand washing shed built?
- It dates from 1933 and, according to the national database, was moved in the mid-Showa period, between 1946 and 1965. It was listed on October 28, 2011.
- What is unusual about the columns of the Osaki sand washing shed?
- Their lower parts are reinforced concrete, and their upper parts are old railway rails joined in a Y shape to support the timber roof.
- How big is the sand washing shed at the Osaki Water Purification Plant?
- It measures 4.9 meters by 3.8 meters, a building area of 19 square meters, and has no walls.
- Can you see the Osaki plant sand washing shed?
- The grounds are normally closed. During the spring opening it can be seen from outside, east of the slow sand filters.
Basic Information
| Name | Sanjo City Waterworks Bureau Osaki Water Purification Plant Sand Washing Shed |
|---|---|
| Location | 4420-3 Nakashin, Sanjo City, Niigata Prefecture |
| Designation | Registered Tangible Cultural Property (Building) |
| Year Designated | Registered 2011/10/28 (Heisei 23) |
| Quantity | 1 building |
| Dimensions | Single-storey steel-frame shed with sheet-metal roof, 4.9 meters by 3.8 meters, building area 19 square meters |
| Owner | Sanjo City Waterworks |
| Public Access | Normally closed as a working waterworks; the grounds may open to walkers in cherry blossom season |
References
- Cultural Heritage Database: Sanjo City Waterworks Bureau Osaki Water Purification Plant Sand Washing Shed (Agency for Cultural Affairs, in Japanese)
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00008839
- Registered Tangible Cultural Property: Sanjo City Waterworks Bureau Osaki Water Purification Plant (Sanjo City, in Japanese)
- https://www.city.sanjo.niigata.jp/soshiki/shimimbu/shogaigakushuka/bunkazai/bunkazai/1740.html
- Sanjo City Waterworks Bureau Osaki Water Purification Plant (Japan Society of Civil Engineers, Niigata branch, in Japanese)
- https://jsce-niigata.com/introduction/article/049/art049.html
Last verified: 2026.09.25
