I wanted to be able to wash the bus and rinse it to be as spot free as possible. There are quite a cew systems on the market which claim to do this. They also seem to cost about the same. That is to say, a small to medium sized filtering system goes for about $350 - i have purchased the "Stain-Less" system. Go here for more details.
http://www.stainlesswaterfilters.com/
Cheers,
Ronald