Drinking too much water in a day can lead to a dangerous condition called water intoxication or hyponatremia, where excess water dilutes the sodium in your blood, causing cells-including brain cells-to swell. This can result in symptoms like headache, nausea, confusion, muscle weakness, seizures, and in severe cases, death

. How much water is too much?

• The kidneys can process about 0.7 to 1 liter (about 3 to 4 cups) of water per hour. Drinking significantly more than this in a short time can overwhelm the kidneys and cause overhydration

• Consuming 8 to 10 liters (about 34 to 42 cups) or more in a day is excessive and can cause kidney trouble and water intoxication

• The CDC advises not to drink more than 48 ounces (6 cups) per hour to avoid risk of overhydration

General daily water intake guidelines for healthy adults:

• Men: About 13 to 15.5 cups (3.7 to 3.9 liters) of fluids per day, including all beverages and water in food

• Women: About 9 to 11.5 cups (2.7 to 2.7 liters) of fluids per day

• These amounts vary based on age, activity level, climate, health status, and diet

Summary:
Drinking more than about 1 liter per hour or exceeding roughly 8 to 10 liters per day can be too much and harmful. For most people, following thirst cues and aiming for around 9–15 cups of fluids daily is sufficient and safe