The most abundant nutrient
Makes up about 50–60% of an adult's body weight. It carries nutrients, removes waste, regulates temperature and cushions tissues.
Solvent for nearly every reaction, transport medium for blood, coolant through sweat, and lubricant for joints.
Everywhere: about two-thirds inside cells, one-third outside.
Drinks of all kinds (including tea, coffee and milk) plus food — fruits and vegetables are often 80–95% water.
Adequate Intake (total water from food and drink): about 3.7 L (men), 2.7 L (women) per day. Needs vary with heat, activity and body size.
Mild dehydration can cause thirst, headache and reduced performance; severe dehydration is a medical emergency.
Drinking very large amounts quickly can dilute blood sodium (hyponatremia), a risk in long endurance events.
Balanced together with sodium and potassium.
The '8 glasses a day' rule isn't based on strong evidence; thirst works well for most healthy people.
General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.