The advice to drink eight glasses of water a day has been repeated so often that most people assume it rests on research. It does not. The figure appears to trace back to a recommendation from the 1940s which noted, in the same paragraph, that most of that water is already present in prepared food. That second half dropped away and the number survived on its own. This does not mean hydration is unimportant. It means the specific figure carries no particular authority, and that thirst, for a healthy adult in an ordinary climate, is a reasonably good guide.
It can be inferred from the passage that the original 1940s recommendation
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Correct answer to question 29 (Paragraph Comprehension): was less demanding than the version now repeated
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The original noted that food already supplies most of that water, so the amount left to drink was smaller than eight glasses. Losing that qualification made the advice more demanding than it began.
Updated: November 2026
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