Hello Barbara, I'm Dr. Deb.
I recently came online and see that your question hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
I can't see where this filter would cause any problems for a cat who likes to drink water from the tap, especially since it's a non-chemical method for altering the characteristics of hard water. The absence of scale in the water is also not worrisome since cats don't need scale in their diets.
I can understand why you might be concerned but I hope that I've reassured you that there's nothing to worry about.
My apologies, again, for the delayed reply. Deb