Rockwood/Flagstaff - travel with full fresh water tank?

A half tank of water would still be spread over much of the tank area even in a sharp turn. In other words, the full weight of the water will not be at the extreme edge of the tank. If there is a noticeable problem, you have an extremely marginal tow vehicle. What would you do if your mother-in-law in the back seat shifts her weight to pass gas?