It is possible to drink too much water. Healthy kidneys in an adult can process anywhere from 20 to 1,000 milliliters of fluid per hour. It's not easy to overload them, but it can happen. Getting too much water, especially in a short time, is dangerous. Symptoms of too much water include weight gain, bloating, nausea, and vomiting. Sudden cases of water intoxication can cause low blood sodium, which can result in headaches, confusion, seizures, and coma.
The International Marathon Medical Directors Association recommends that athletes drink no more than 31 ounces of water per hour during extended exercise.