Kusari toi (sometimes translitered “doi”)—the Japanese characters are 鎖樋 which translates literally as “chain gutters”—are known in English as rain chains. They are used in Japan as downspouts to direct rain from a gutter to the ground, where it either flows into a gravel or pebble bed or into some sort of catchment. Rain chains are traditional on Japanese houses and temples, but they’re also sometimes seen on midcentury modern houses, not surprising considering the influence of Japanese house design on modernist architecture. And because of their ecological value – they direct water back onto the property, instead of into storm drains – they are becoming more popular on all types of houses. It’s said that their purpose was traditionally largely decorative, but that’s not entirely true, contrary to what many house inspectors think. Chains actually do function perfectly well as downspouts. In my experience in BC, rain chains have usually just been made from simple heavy chain (see my video in the previous post) but they are also sometimes made from a series of metal cups strung at intervals on a chain. (See example in copper, above – note that for some reason this one is missing its catchment.) With the latter type, water overflows each cup and falls to the next, producing the sound of a fountain or brook. In Japanese gardens greater attention is paid to sound, and rain chains are part of that sensitivity. They do make a beautiful sound. I for one really dislike the clumsy ticking of water in metal downspouts.
Below is a rain chain at an Eichler house in California. Here the water runs into a traditional Japanese pebble pit.
More information here, and see also here and here. And update: see Anna’s rain chain on a traditional heritage NY State house here. You don’t have to have a Japanese or midcentury modern house to have a rain chain.