I have no clue! I just make sure I am carrying a small water bottle with me all day, and every chance I get to fill it up I do. It's a lightweight bottle that fits nicely in my purse, laptop bag, or large coat pocket.
The weirdest things are my other drinks, because they're things I would not normally consume -- pregnancy is so odd! I am normally a huge coffee addict - the snobby "strong black coffee from freshly roasted beans" kind - but I haven't had any in a while now I don't even crave it one bit; the caffeine cravings were gone after 2-3 days. Nowadays the only time I drink a bit is when I can't poop at all (which I solved with bran flakes since my last cup of coffee a month ago). I usually have a glass of apple juice sometime during the day, even though I am not typically a big fan of it and prefer OJ (OJ now seems repulsive). The last two weeks, every other day or so, I have a hot chocolate in the afternoon - the weather has turned and it's nice to go do my work a local cafe. I try to make sure I get it with lactose-free low-fat milk or soy milk if they don't have that; I've always had dairy issues but figure the baby needs some calcium! Very occasionally I have a mint tea or a fresh fruit smoothie if it's available. Mmmm smoothies are AMAZING when pregnant.
I also eat a lot of fruit. I carry apples, clementines, grapes, etc with me for snacking.
I must be doing something right, I pee A LOT.