How much water should I drink daily?

I've heard of the standard "8 cups a day" but 64oz doesn't seem to cut it. I'm 6'4" 240lbs and I drink about an 8 ounce cup of coffee everyday and in the habit of adding salt to virtually everything I eat. I don't get as much vegetables like lettuce which are full of water as I probably should but I don't sweat much. The water just seems to go right through me regardless of how much I drink.