It's really not necessary to drink that much water. If you're that thirsty and you want to drink that much water, by all means do so, but if it's struggle there's no reason to drink that much. Also, in terms of staying hydrated, just about any liquid counts, even coffee, soda, and alcohol. And all food has water in it too (even bread is about 30% water) and that water also helps you stay hydrated.
There was a great interview in June 2008 Nutrition Action newsletter on this. They interviewed Dr. Heinz Valtin, a physician who authored several widely used medical textbooks on kidney function and water balance. According to Dr. Valtin, there was really never any basis for the myth that you have to drink eight glasses of water per day or the theory that once you are thirsty you are already dehydrated. Dehydration is measured by how concentrated the blood is. According to Dr. Valtin, thirst sets in when the blood is about 2% concentrated; dehydration doesn't occur until the blood is about 5% concentrated. So drinking when you are thirsty is a pretty good way to make sure you are properly hydrated.
And you can drink whatever you want--at least for purposes of staying hydrated. There are other reasons not to overdo it on coffee, soda, sugary drinks, or alcohol, but staying hydrated isn't one of them. The idea that coffee is a diuretic is also disputed in the interview.
Another good article on how much water you need to drink is
Fluid Fundamentals on CookingLight.com.
I drink very little straight water. I eat a lot of veggies that are in high in water content and I drink coffee, tea, and non-carbonated diet beverages (like Crystal Light). I don't drink carbonated beverages because I think they cause digestive issues for me, not because I don't think they're a perfectly good source of water. About the only time I drink plain water is when I work out and it's only because I don't want anything but water in my water bottles (they're too hard to wash if I put other stuff in them).