The amount of water a person can safely drink varies depending on individual factors such as health, activity level, and environment. Generally, the kidneys can process about 0.8 to 1.0 liters of water per hour. Drinking more than this amount over several hours can overwhelm the kidneys and lead to water intoxication, a dangerous condition caused by diluted blood sodium levels (hyponatremia), which causes cells to swell, including brain cells
. Symptoms of water intoxication typically appear after consuming more than 3 to 4 liters of water in a few hours. Severe cases can cause confusion, seizures, brain swelling, coma, and even death, though such cases are rare and usually linked to extreme physical activity or underlying health conditions
. For daily hydration, the U.S. National Academies of Sciences suggests an adequate fluid intake of about 15 cups (3.7 liters) for men and 11 cups (2.7 liters) for women, including fluids from all beverages and foods. Drinking according to thirst and monitoring urine color (light yellow indicates good hydration) are practical guidelines
. In summary:
- Kidneys can safely remove about 1 liter of water per hour.
- Drinking more than 3-4 liters in a few hours risks water intoxication.
- Daily water needs vary but average around 2.7 to 3.7 liters total fluids.
- Overhydration is rare but can be fatal if severe.
Extreme cases of water poisoning have involved drinking around 6 liters in a short time, which can be lethal for a 75 kg person
