I ususally pack a Britta pitcher in my suitcase. The night before a park day, I fill our bottles half way with filtered water and put them in the freezer. The next morning, I fill the rest with the filtered water. Before we leave, I start another set of half filled bottles in the freezer to exchange midday when we return for our midday rest. We have cold water almost all day. Some days, we purchase additional water in the parks with snack credits.
Another thing I pack is a 2 quart plastic pitcher. (I usually stuff it with socks or such in my suitcase) I also pack a container of Kool-aid and a spoon. In the evenings when the kids are thirsty and want more than just water, the filtered water and Kool-aid mix always make them happy.