I've never understood traveling without a full tank of water. I boondock during the winter, and FHU during the summer; I ALWAYS fill my water prior to leaving home. You never know when the campground you're headed to may have a problem with their water system. You never know when you may be broke down for a few days and need to have water available. You never know... Unless you are really close to your GWVR or GCWR, there's really no downside to it. 250lbs is not going to make any measurable difference in handling or MPG. I don't know anyone in our group (at least 7 rigs) that doesn't travel with a full tank.
My last RV, a '88 Jamboree class C, had a 30 gallon tank. With a family, we had to be really careful when boondocking. I now have a class A; sure love the 84 gal of fresh water!!