When I first went to the health club and the trainer there said I should drink a gallon of water a day, I actually laughed at her, I thought she was joking! But now,I won't say that I get a gallon everyday, but, I genereally get at least 100 oz. I had to start out slowly, with 64 oz a day, and work myself up, and I still have to run to the restroom about every 60-90 minutes (luckily at my job they don't care LOL) but I just kept slowly drinking more and more, and now if I only get 64 oz, I can tell. It also helped that I cut out soda, and now only drink a cup of coffee, water and a large glass of milk everyday. I keep a 1 liter water bottle with me at all times, and I fill it from the drinking fountain, or faucet. It is to the point now, that I even take it shopping with me, and I feel like have forgotten something all day when I don't have it.
Just start out slowly, and let your body get adjusted to it, if you keep a bottle with you and just sip it al day long, you'll be amazed at how much you actually drink. You'll see that over time, it gets easier and easier!