I wouldn't worry about getting too much, most people do not get enough, even when they THINK they are getting adequate amounts.
Drink enough so that your urine color is clear throughout the day....then you know you are staying well hydrated. Also, you should never be "thirsty"...by that time, it's too late. You'll eventually be able to gauge what is enough, and stick with that....but it also will vary depending on air temperature, climate, your activity level for any given day/hour, etc..
The easy thing to do is just have water with you all the time, then you are prepared for any situation that may arise.
