Before dams were built, Okinawa suffered from water shortages. Although Okinawa receives a lot of rain, much of the islands are covered in Ryukyu limestone, so water easily drains into the sea and is difficult to retain.
Because of this, planned water outages were once common, and people used to build tanks outside their homes to collect and store rainwater.
Interestingly, this tensui was considered superior to ordinary water, and people would even drink it when they were sick. This was only a few decades ago, yet it shows how different life was compared to today.
by Away_Trash_2156