Why does Chinese medicine say to drink warm water?

The tradition thinks of the stomach as a pot and the spleen as the fire under it. Food goes in, is cooked, and the steam of it, the tradition’s word is essence, rises to feed the rest of the body. A pot works by being warm. Pour cold water into it at the wrong moment and the cooking stops until the fire has caught up, and in a body whose fire is already low it may not catch up before the next meal. That is the entire argument, and it is a good one for the person it was made for.

It was made for the cold-and-tired person, and for everyone at mealtimes. It was not made as a law of physics. The classics themselves ask for something milder than the modern rule: not hot water, but water that is neither scalding nor chilling. A healthy adult who drinks a glass of cold water on a July afternoon has broken nothing, and a person who scalds their throat with boiling tea every morning has followed nothing.

The line the advice rests on is in the Lingshu, in a chapter of instructions handed from teacher to pupil. It is about temperature in both directions, and the word at its centre is the middle.

The pot image comes from the Suwen’s account of what happens to a drink. It enters the stomach, its essence is sent up to the spleen and on to the lung, and what is left goes down to the bladder. Every step in that sentence is a step that the tradition believes warmth helps and cold slows.

And the rule for the damp person, who has water pooled in the middle already, is in the Jingui Yaolüe of the second century, in six characters that every later physician learned by heart: what has pooled is settled with warmth.

The advice is not the same for everyone, and the tradition never said it was.

Two things should be said plainly. The first is that the Chinese habit of drinking boiled water was, for most of history, hygiene: boiled water was safe water, and warm was the temperature it came at. The tradition made a virtue of it, but the virtue came second. The second is that for a healthy adult there is thin evidence either way about warm water against cold, and we do not claim otherwise. The tradition’s claim is narrower and better: that a cold, tired middle is slowed by cold drinks, and that everyone’s meal is sorted better warm. That claim it has kept for two thousand years, and it is the one we make.

• A cup of warm water on waking, before anything else, sipped. It is the oldest morning habit the tradition has.
• No iced drinks with meals, in any season, for anyone. The sorting of the meal is what the rule protects.
• Warm, not hot. Tea you have to wait for is tea the tradition would not drink; scalding is its own harm, and the classics name it.
• Sip through the day rather than gulping a pint at once. The tradition is wary of flooding the middle.
• In summer, room temperature counts as warm. The rule is about the chill, not the heat.

None of that is a promise, and we make none. It is the floor, and the cup at meals is the plank.

• Ginger 生姜, two slices in the morning cup, for the cold-and-tired. Mornings only.
• Tangerine peel 陈皮, a piece in hot water after meals, for the heavy-and-damp and for anyone who ate too much.
• Jujube 大枣, three split in a pot of water, simmered, for the tired and for the evening.
• Chrysanthemum 菊花, steeped and allowed to cool, for the hot-and-dry, in the afternoon.