No chugging a gallon of water or milk won't kill you. maybe tequila or something but definitely not water or milk.  Every hour, a healthy kidney at rest can excrete 800 to 1,000 milliliters, or 0.21 to 0.26 gallon, of water and therefore a person can drink water at a rate of 800 to 1,000 milliliters per hour without experiencing a net gain in water. so after 4 hours you have peed out all the water you drank.