Filling the water tank while on the road

So far every place that I've ever 'dry camped', they've always had a place that I could fill when I arrived. In a couple weeks I'll be heading to a place that doesn't have that option. I don't want to tow the extra weight for the entire trip. I want to fill close to my destination point. Do truck plaza's have water available at the diesel islands? I'm just looking for any options. I know many Flying J's have a RV island but the one closest to my destination does not.