I almost always carry 2, count them 2, water skins. One full of, duh, water, and one empty. (Of course, I do that because few others think to bring an extra, empty, waterskin.) If I'm feeling very froggy, I'll sometimes tote along an empty flask. (Or I'll get the flask instead of the extra waterskin.) It sounds silly, stories and legends are just filled with TOO many interesting magical liquids not to be ready with something to fill. I don't want to have to empty out my own waterskin, because I hate not having water for myself... So I always have something extra to carry liquids. You can have the extra waterskin prefilled with water or wine, but that will add to your encumberance.