It should be the upper water, which is light and floats on it, and the lower water has many impurities, so it sinks below. The ancients in China said that the best way to make tea is rain. When the environmental pollution is small, you can drink rain in places where it often rains, followed by spring water, river water and well water, because well water does not flow. There is an incisive exposition on the water for making tea in A Dream of Red Mansions. You can learn about it. Before the liberation of Chengdu, the teahouse also had the practice of washing water, that is, taking water from the middle of the river, constantly stirring it with well water, and finally taking only the upper water to make tea. It is said that the effect is also very good.

The ancients said: running water does not rot. Flowing water carries less corrupt substances and the water quality is purer. Well water is rich in sediments. Of course, well water is better than tap water now, but well water is easier to be polluted and more difficult to detect.

Spring water now generally refers to mineral water, and direct drinking can supplement some trace elements in the human body. However, if it is used to make tea, some trace elements will react with some components in tea, affecting the effect and final taste of tea, so it is not the best.

Tianshui, also called rootless water, generally refers to water falling from the sky, including frost, dew, snow and so on. This is described in detail in A Dream of Red Mansions, which generally refers to rain. According to the understanding of the ancients, the water on the ground was evaporated into clouds in the sky by the high temperature of nature, and the clouds in the sky turned into water and fell to the ground when they met with low temperature. It can be said that it is a collection of the essence of heaven and earth, and life can only be nurtured after sex and rain turn. It's ok to drink this kind of water. From a modern point of view, rainwater is a kind of distilled water, which is used without impurities, but now rainwater is afraid to drink it casually.

There is a story that Su Shi heard that Wang Anshi was going to cross the Three Gorges and asked him to bring him some water from the Middle Gorge. But Wang Anshi forgot to take water when he crossed the middle gorge, and he remembered it only when he got to the lower gorge. He thought you wanted water anyway, but he didn't know if he brought it for you, so he took water from Xiaxia and gave it to Su Shi. When Su Shi used it to make tea, he said it was not the water in the middle gorge. Wang Anshi was surprised and said you.