A Ming Dynasty document, written conversation of Plum Blossom Herbal Hall, crystallizes the essential importance of water for tea. It states:⁠

“The inherent quality of tea must be expressed in water, when a tea that is an eight meets with a water that is a ten, the tea is also a ten! when water that is an eight pair with a tea that is a ten then the tea is just an eight” ⁠

Dr. Ming Wu uses the best water when he is making his tea, water of the highest quality expresses the best qualities of a tea infusion. Therefore, when lower quality tea is brewed with high quality water, the resulting infusion is of high quality. On the other hand, when superior quality is brewed using inferior water, the resulting infusion is inferior. Water directly affects the flavor, aroma, and color characteristics of a tea infusion. Superior quality tea when brewed using inferior water essentially ruins the tea.

Lu Yu of the Tang Dynasty (733-804 AD) said in his book "Tea Classics": water is the mother of tea, which expresses the importance of using high quality water for good tea.⁠

Ancient Chinese classified water based on the apparent source: either from the sky or earth. Waters from the sky were called “heaven spring”. Sky waters included rain, snow, hail, frost, and dew.

Earth waters included spring, river, and well water.⁠ Lu Yu said in his "Tea Classics": spring water is preferred, next is river water, and well water is of the lowest quality of the three.

Reference：

The ancient art of tea - wisdom from the old Chinese Tea Masters by: Warren Peltier