It seems like the recommended dose I've heard too. Maybe a little less 70-80. I have the opposite trouble I find I constantly drink too little every day, but hey I'm still standing.
There is often more water in food than you might first think. Take cucumber for instance. It’s 95% water! We boil pasta and rice so some of that water is still in the food when we eat it.
Found this on answers.com (via google mind you)
“Can You Really Drink Too Much Water?
In a word, yes. Drinking too much water can lead to a condition known as water intoxication and to a related problem resulting from the dilution of sodium in the body, hyponatremia. Water intoxication is most commonly seen in infants under six months of age and sometimes in athletes. A baby can get water intoxication as a result of drinking several bottles of water a day or from drinking infant formula that has been diluted too much. Athletes can also suffer from water intoxication. Athletes sweat heavily, losing both water and electrolytes. Water intoxication and hyponatremia result when a dehydrated person drinks too much water without the accompanying electrolytes.”
Rest of the article: http://chemistry.about.com/cs/5/f/blwaterintox.htm