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Thesis
Section 1 is not really about “其水用山水上江水中井水下”; it is about how Lu Yu turns tea from a local product into an object of argument.
Text
“For water: mountain spring is best, river water next, and well water lowest.”
Context
古人择水：山泉水最优，江水次之，井水最下。核心是"活"与"清"。
Evidence
- Collation: 各本一致。此句为全书最广为引用的择水标准，后世茶书多沿其说。
- Existing readings: 吴觉农指出：陆羽"山水上"之论影响千年，其内核是"活水为上"——山泉活水含氧高、杂质少；现代水质科学证实，矿物质适度、溶氧充足的活水确实更宜茶。
Analysis
Formally, the section gives a judgment, adds material detail, then returns to human practice. 古人择水：山泉水最优，江水次之，井水最下。核心是"活"与"清"。 That is why the Classic of Tea reads as an argued book rather than a miscellany.
Conclusion
The section does not give a universal rule. It demonstrates a method: read the text, the annotation and the Tang context together before making a modern claim.
Source: The Classic of Tea, Chapter V · The Brewing, section 1; the original is in the public domain.
Get the character right before the taste.