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I once visited the Grand Historian in Lingtai and observed the water dripping from a bronze clepsydra (water clock). The Historian summoned the water keeper, saying, "This water has circulated three times; as the water becomes slippery, the leakage accelerates, causing timekeeping errors. It should be replaced with fresh water." I suddenly realized: Water from all over the world is the same when used to extinguish fire or to moisten withered things. However, its nature changes according to the land, and its quality shifts according to what it contacts. For instance, washing brocade in the rivers of Shu makes them bright; cooking paper mulberry bark in the waters of Jiyuan alters their properties. The pools in Nanyang are infused with chrysanthemum, and the people there enjoy longevity; the streams in Liaodong connect with ginseng roots, and the people there have good hair. Mountains in Jin produce alum stone, and the spring water can cure smallpox; at the foot of mountains in Rong, sulfur lies hidden, and the hot springs can treat leprosy. The Yangtze River is suitable for brewing wine, and vegetables from Huai are suitable for making fermented rice wine. Brine from Cangzhou can produce salt, and water from A Well can make gelatin. Washing dirt with dirt removes impurities; irrigating fields with bitter water promotes crop growth. Goiters dissipate in the waves of kelp and seaweed; phlegm is broken down by the juice of Pinellia ternata (Banxia). Swallowing ice water stops cholera; drinking flowing water unblocks urinary retention. Washing eyes with snow water reduces redness; bathing skin with saline water dries up sores. Vegetables are made into minced relishes; iron is forged into plowshares; yeast turns grain into wine; cypress trees are processed into vinegar. There are thousands of sources and varieties, too numerous to describe fully. Even well water, though from the same source, has many names. How much more so for other waters? When poured back, it is called "Reverse Flowing Water"; when emerging but not yet released, it is called "Rootless Water"; freshly drawn at any time is "New Drawn Water"; drawn first at dawn is "Well Flower Water". Water from a single well has different functions. Is it not essential to select water carefully when decocting medicines to enhance their therapeutic effects? Once, a patient suffered from urinary obstruction, which many physicians failed to cure. I substituted long-river rapid-flowing water, boiled the prescribed medicine in it, and after one drink, urination was immediately restored. Yuanchou remarked, "What a profound theory!" Recently, reading the *Ling Shu Jing* (Spiritual Pivot), I found that Banxia Tang (Pinellia Decoction) for insomnia uses eight liters of flowing water from a thousand li away, tossed ten thousand times, taking five liters of the clear liquid, and cooked with reed fire. This perfectly aligns with my discussion. Thus, I know that Hezi (Zhang Congzheng), in his medical practice, finds therapeutic methods in every matter and object. Just as Zhang Chaoshi's cursive script is unparalleled, derived from Gongsun Dama Niang's sword dance, requiring great mental effort. Those who use water in medicine thereafter should take Hezi's words as their standard. Therefore, I composed this chapter on Water Analysis.