Works on Water
     Lu Yu was the first person to discuss and evaluate waters used for brewing tea in the writing called "Tea Classic". He pointed out that flow mountain water was the best, river water was the next and well water was the worst. Among waters from the mountains, water from springs stone ponds and murmuring streams were the best.
 On this basis, tea scholars of the later ages summed up the standards for evaluating water from the nature by the following qualities: clarity, cleanliness, light, sweetness , flow.

 Clear: the water should be colorless and transparent, without precipitates.
     Light: Emperor Qinglong measured spring waters everywhere using a special silver "dou" (a measuring container). He concluded that spring water from Sanquan Mountain of Beijing was the lightest and wrote an inscription for it: "The First Spring under Heaven". Today, the evaluation was understood by calcium and magnesium content analyzed with modern technology (i.e. hard water or soft water).
     Sweet: It referred to the fresh taste of water.
     Cold: The water should be cold before heated. The ancient people thought it estimable to cook tea in snow water.
     Clean: The water should be free from dirt or contaminants.
     Flowing: Su Shi's poem reads that "Fresh water should be heated from running water". Tang Geng of the Song Dynasty described in his "Tea Competition Notes" that water could be from either river or well, the important thing was that it was flowing". Stagnant water should mot be used.