Use good water

You need good water. "D'uh" you say, but there are many different types of water. Never use bore or dam water as these are high in nutrients and the salinity content (salt = rust) may be questionable. Even if you have had your bore checked for salinity levels, think twice before you take to your pride and joy with the offending water, salinity levels fluctuate. Certain areas of Australia, like Adelaide for a classic example, have 'hard' tap water, this is where, for reasons only the water board really know, the water is high in mineral content. Hard water, like acid rain, is prone to leaving very defined water spots on your paint if it dries. Regardless of your water source, as long as it is not dam or bore, it will do the trick, but if you have the option of using 'soft' water, and the best of these is pure rainwater, go with it every time. We have special, double filtered tanks of rainwater just for washing the cars. Considering we live in a semi-rural area, this is not as extravagant as it sounds. They also double as fire fighting supplies and fantastic rogue bush-turkey deterrents.