You really have to overdo it to take in too much water. Basically if you drink at a normal human pace throughout the day you'll be completely in the clear. A gallon a day is nothing.
In that article it said somebody drank 3 liters before a race, and more in the early stages or something. That's like a gallon in and hour or two possibly, which could be problematic. But for the rest of us, you really need not worry about water intoxication. As long as you're not sitting at your desk slamming it like no tomorrow, everything will be fine.
