For those advocating the use of a "water thief", keep in mind that many USFS and State Park campgrounds have water hand pump or faucets that such a gadget can not be used on. They are specifically designed to prevent that.
I tried the "1/4 tank of fresh water for the trip, fill at destination" scenario once years ago. I found no benefit from doing so; the handling over the mountain pass wasn't any better, the fuel economy didn't show a significant improvement, and the hassle of filling the water tank at the destination wasn't worth the trouble, IMO
Of course, YMMV. We each have to do what makes us happy.
Good luck.
