I've heard that a good rule of thumb is to take your weight (# lbs), divide that in half, and that's the number of ounces of water you should drink each day. So if you're 200 lbs, that would be 100 oz., or 12.5 8oz glasses a day.
The general recommendation tends to be about 8 8oz glasses a day, but I have seen it as low as 6 glasses.
I realized for me it is easier to drink from big bottles of water and count those, rather than smaller bottles. I have a couple of 24 ounce bottles, and a 64 ounce bottle.
I fill that bottle from my Brita and take it to work each day. My goal is to drink one of those each day at work, plus the 24 ounce bottle before and after work. That's 14 glasses a day!
I actually find I drink a lot more water during the week, since I drink so much while at work. I also like to keep water with me in the car. Basically, I drink water when I'm bored or stuck somewhere like work! Then it's less of a chore.