In villages where the mountains of Japan meet the plains near Kyoto, a water system called the riverside method, or kabata, has run households for over a thousand years. Spring water is piped straight into a basin built into each home, straddling the line between indoors and outdoors, and from there it serves every domestic task: rinsing pots, washing vegetables, communal dishwashing. Carp kept in the tanks finish the job, picking clean even the greasiest pans before the water flows back into the local streams. The film follows Sangoro Tanaka, an 83-year-old resident who has tended this system for decades, as he moves through the seasonal rhythms that still govern these communities. The camera stays close to the mechanics of the setup, showing exactly how a single channel of water gets reused, filtered, and returned to nature without waste. Produced by the BBC, the film treats satoyama less as scenery and more as an engineering tradition, one built entirely around keeping people and the surrounding wildlife on the same water supply.