Water Softeners and Rainbow
I have used first my old Rainbow SE and the last 3 years the new Black Rainbow for a total of 8 years with a water softener and no damage, so I think you should be ok.
I use only the Rainbow daily, so they both have seen a lot of basins of softened water over the years. The soft water has also been used in the Rainbowjet, sprayer and Aquamate attachments with no damage.