Unless you are in the middle of a desert, not bringing gallons of bottled water is OK. Water from some natural sources is safe for drinking (knowing which kind is important here); being able to boil water makes things even better. On the other hand, I myself have made day-long trips without consuming any water at all; looks like it is not far from truth that one can easily survive without water for a few days. (I would also note that to me it seems that for some people who I observed constant drinking water is more of a bad habit than a necessity.)