How much water is too much water to drink?

Answer 1

On average, an adult human needs to consume 64 ounces of water in a day, which works out to a half gallon of water from all sources. Drinking more than a gallon of water a day can cause serious damage to your kidneys by washing out all the salt that allows you to concentrate urine and maintain proper salt levels in the blood.

Drinking several gallons of water a day can cause water poisoning pretty quick, and incidentally people have died from voluntarily drinking too much distilled water.