Does Everyone Need Exactly Eight Glasses of Water?
There is no universal scientific rule requiring every person to drink exactly eight glasses of plain water each day. The popular “8×8” advice is a convenient rule of thumb, not a separate target that fits everyone. Needs vary with diet, body size, activity, climate, pregnancy, health, and other circumstances.
The U.S. National Academies list adequate intake levels for total water for adults aged 19–30 of about 3.7 L per day for men and 2.7 L for women. This includes water from all beverages and foods, not only glasses of drinking water; these are population reference values, not a requirement to drink that volume as plain water. The “8×8” advice should not be confused with those values.