How Much Water Do You Actually Need?

The eight-glasses rule is memorable and roughly the right order of magnitude, which is about as much as can be said for it. It does not account for your size, the weather, what you ate, or what you did that day.

A more useful frame

• Drink steadily rather than in large infrequent amounts.
• Anchor it to things you already do — with each meal, on arriving at your desk.
• Food counts. Cucumber, watermelon, soup and herbal tea all contribute.
• Hot days and hard exercise raise the requirement, sometimes considerably.

Why it matters for lymphatic flow

Lymph is mostly water. When you are short of it, the fluid is thicker and harder to move; when you are well hydrated, it stays thin and moves easily. This is the least complicated lever you have.