I have a 24 oz water bottle that I bought at Kitty Hawk Kites, and I drink the thing probably 4 times on an average day during the week - one in the morning on my way to work, one during lunch, and two more in the evening. If I'm drinking alcohol in the evening, I'll drink more. I find that if I'm taking in alcohol, and I don't drink enough water, that I don't sleep. Keep in mind that I'm not getting drunk, just having 2 - 3 glasses of red wine.
During the summer, I will drink more, and when we're on vacation on the OBX, I will easily take in 200+ oz in a day. 50 oz while riding the bike, and then because we typically drink more wine, I'll drink even more water.
The only time I drink plain water, however, is when I'm riding my bike. I add the orange Mio, or orange Crush water enhancer.
I think it's hard to determine what an appropriate amount is as individuals vary by their weight/activity level and other things. The way I can tell if I'm not taking in enough water is that I'll wake up in the night with my calves cramping up.