We have well water at the home place in Luray, VA, and think it superior in taste to most campground water. Therefore, we always fill up our fresh water tank prior to leaving, and use it for drinking and cooking. We only use the city water at campground for showers and such. We have never had a problem with the extra weight on the tires. If you look at the spec on your unit, there should be a max gross weight, and if you have a full or half-full tank of water, it might reduce the amount of weight available for clothing, food, people, and so forth, but unless you are already close to that max gross weight, there should be no problem. Tires will probably be rated for a little more than the max gross weight, regardless of what is adding that weight. Hope this helps.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.