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Thesis
Read through modern tea science, “其水用山水上江水中井水下其山水拣乳泉石池漫流” is not a lab result but a set of variables: cultivar, soil, light and plucking standard.
Text
“For water, mountain spring is best, river next, well lowest. Of mountain springs, choose the milky fountains that seep from rocky pools; avoid rushing, churning torrents.”
Context
乳泉：石乳般的泉水。石池漫流：从石池缓缓流出的水。瀑涌湍漱：奔涌湍急的水。
Evidence
- Collation: 此句为五之煮名句，各本一致。吴觉农注："乳泉石池漫流"指流速和缓、杂质沉淀后的活水。
- Existing readings: 吴觉农指出"瀑涌湍漱勿食"极有科学眼光：急流之水挟带泥沙与气泡，杂质多、口感糙；缓流石池水经砂石过滤更清冽——"静水流深"正合好水标准。
Analysis
Modern tea science would split “其水用山水上江水中井水下其山水拣乳泉石池漫流” into cultivar, soil, light and plucking variables. 吴觉农指出"瀑涌湍漱勿食"极有科学眼光：急流之水挟带泥沙与气泡，杂质多、口感糙；缓流石池水经砂石过滤更清冽——"静水流深"正合好水标准。 They remain testable, but only with their conditions attached.
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 IV · The Vessels, section 6; the original is in the public domain.
Experience should be explained, not mystified.