How Much Water Should I Drink a Day?
Understand adult total-water references, why needs vary, and why no single daily amount fits everyone.
There is no exact number for everyone
Water needs vary with age, sex, pregnancy or breastfeeding, activity, climate, health, diet, and other circumstances. The National Academies uses Adequate Intakes rather than an RDA because evidence does not define one requirement for every person. An AI is a reference point, not an individual prescription. National Academies summary.
Adult references describe total water
For healthy adults ages 19–50, the National Academies lists 3.7 L/day for men and 2.7 L/day for women as total-water AIs. They include drinking water, other beverages, and water in food—not plain water alone. Life-stage values differ during pregnancy and lactation.
Activity, heat, and illness matter
The CDC notes that water needs may rise with heat, physical activity, fever, vomiting, or diarrhea. Medicines and chronic conditions can also affect fluid balance; a clinician may recommend a restriction or a different plan. CDC water overview.
A calculator can show a heuristic
The site’s adult tool uses 30–40 mL/kg/day to display a broad estimate. It is not a clinical formula or universal recommendation. Food and other drinks contribute, and weight alone cannot capture every health condition.
Common questions
Do I need eight glasses of plain water?
Not necessarily. Eight glasses is not a universal prescription; official reference values concern total water.
Does food count?
Yes. The National Academies total-water AI includes water from food and beverages.
What if a clinician gave me a limit?
Follow that individualized plan rather than a general calculator.
Sources and further reading
Sources support the specific guidance described above. This page is general information, not diagnosis or individualized medical advice.