You Are Mostly Water

About 60% of your body is water. Your brain is roughly three-quarters water, your blood is about 90% water, and even your bones are close to 30% water.

Losing even a small fraction of your body water — well before you feel thirsty — is enough to dull how you think. Reaction time slows, mood dips, and concentration drops in ways researchers can measure. The unsettling part is how normal it feels.