You gotta have water, but don't drink so much so quickly and be sure you're getting enough electrolytes.
Proper hydration and intake of electrolytes are necessary for maintenance of homeostasis. And severe water and electrolyte loss can occur due to excessive sweating, vomiting or diarrhea. If water is replaced by plain water without electrolytes, then body fluids can become even more dilute. For this reason, oral rehydration therapy solutions include a small amount of table salt to avoid body fluid dilution.
Water intoxication occurs when a person consumes water steadily and faster than the kidneys can excrete the water or when renal function is poor. The water accumulates in the body, the excess causes cells to swell, which may produce convulsions, coma and death.
No scientific consensus has been reached on how much water should be consumed daily. The safest recommendation is half your body weight in ounces (e.g. 100 lbs = 50 oz). Drink a little more if you're losing more water daily due to exercise or if it's bloody hot, like in Arizona.
Tortora GJ, Derrickson B. Principles of Anatomy and Physiology, 11th ed; 2006. New York: John Wiley & Sons; p1041.