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.
Post# 298475 , Reply# 2   9/15/2014 at 16:33 (3,510 days old) by hydralique(Los Angeles)  
Many homes with a water softener system have some non-softened taps too. Most people prefer the taste of non-softened water so there may an extra cold tap in the kitchen and also non-softened water for the icemaker. Toilets may be non-softened as well.
It is much better than none softened water. It makes the water wetter if that makes sense. I could explain it to you chemistry talk but I don't want to bore you with that.