Water poisoning or water intoxication is a condition where someone drinks too much water in a short period of time and their cells become imbalanced due to a loss of sodium. It is a serious condition but extremely rare.
General guidelines suggest that you shouldn't drink more than 27-33 ounces of water per hour. This means drinking a gallon of water in an hour wouldn’t be recommended.
Any type of water challenge could potentially be dangerous and it is always best to listen to your body.