WZ,
The shielding referred to in the rulebook applies to gas tanks & lines. A water tank will require no shielding. A thought about having hot water in the driver's area - maybe not such a good idea as scalding can result. Most cars will have the water tank in the rear and outside of the driver's area. If the tank is mounted low and securly, adding or subtracting water is a good way to adjust ballist(sp) and weight distribution.
Good luck at the salt.
Dan