we have hard water where i live, got a water softner hooked up, and i only wash my truck with that water, it works so much better,hook a hose up to the sink inside to wash my friggin truck, but it only deserves the best
It's not really "salt water". The salt is used for a chemical reaction to dissolve the hard minerals in your water so that you don't get those rings on the finish that especially show on dark colored paint.
Hot water is more conductive to quick evaporating. And it also keeps your hands warm like when I lived in Idaho -10 degrees. And needing to wash the truck weather. Other than that the hot water is no benefit. Ambient temperature is best and as pure as possible is the greatest benefit. Of course you don't spray cold water on a hot windshield or vs. versus. And the same flex occurs to your paint but, it is much less flex susceptible.