Okamoto Family Water Purification Tank

A Concrete Filter Tower From the Early Shōwa Years

The Okamoto Family Water Purification Tank (岡本家浄化槽, Okamoto-ke Jōkasō) is an early Shōwa-period reinforced-concrete water filter at Mori in Ozu Town, Kikuchi District, Kumamoto Prefecture, listed as a Registered Tangible Cultural Property on 23 August 1999. It stands at the eastern edge of the Okamoto compound between the main house and the stable, rises to a maximum height of 4.3 metres, and carries registration number 43-0035, the last in the run of ten.

The Japanese name, jōkasō, is today the ordinary word for a household septic tank, but this structure did something else. According to the Agency for Cultural Affairs, it pumped up water from an irrigation channel, and later from a well, and filtered it through charcoal and sand. It cleaned the water the household used, rather than treating what it discarded.

In form it is a stack of concrete cylinders built up one on another. Water raised to the top would have worked its way down through layers of charcoal and sand, emerging cleaner at the bottom.

A Record of Everyday Modernisation

The Agency notes that installations like this were once common in the district but that few now survive, and it values the Okamoto Family Water Purification Tank as a structure that documents the modernisation of daily life. It was registered as difficult to reproduce.

Among late Edo gates and fences and Meiji storehouses, a column of grey concrete cylinders looks out of place. That is exactly its value. It shows that the Okamoto family did not freeze its compound in amber but kept living in it and upgrading it, installing a pump and a filter in a corner of a samurai-era property.

Its commonness once is part of the story too. Ordinary equipment is the first thing to be demolished when it stops being useful. The more widespread something was, the less likely it is to survive, which is what makes this single survivor a record of how people in the district lived.

What to Look For

The stacked-cylinder profile and the 4.3-metre height are the things to register. Standing between the single-storey stable and the two-storey main house, the Okamoto Family Water Purification Tank adds one grey vertical line to a skyline otherwise made of tiled roofs.

Seeing the Tank

The tank stands inside a private compound at its eastern edge, between the main house and the stable, and it is not open to visitors. The grounds cannot be entered, so any view is from the public road.

The stable occupies the southeast corner of the plot along the southern road, and the tank stands north of it, inside the property. Whether it can be seen from the south road depends on how the surrounding buildings and fences block the view. Photograph from the road only and keep the camera off the living quarters.