Why do you want to swim on Tanabata?

Our tradition is that swimming on Tanabata can get rid of many diseases, without sores, prickly heat and smooth skin. People in rural areas will take some water from the mountain stream and store it before the sun comes out on Tanabata every year, which can be used as trauma medicine. The mountain stream doesn't change its taste for a year, but at other times it will stink after a long time. Some really can't be explained.