You may be seeing mineral build up or scale particularly if your water has lime or calcium in it.
To get lime off you can try a solution of one part vinegar to three parts water. Let the bowl or fountain soak in the solution then brush to loosen. Rinse well with clean water. For fussy cats you will have to rinse extra clean!
I'd try it on the bowl first to see if that solves the problem and then if you know that mineral build up is the issue, you can plan to clean the fountain the same way (but check directions on fountain cleaning).
You may find the reviews on this page about the Drinkwell fountain and cleaning it useful info
http://www.amazon.com/Drinkwell-Pet-Fountain-for-Cats/dp/B00063446M/ref=pd_sbs_k_1/103-6633753-9466240?ie=UTF8
one mentions the bacteria that isn't harmful that can grow in any water bowl.
Hope this helps you!
Edited by NHolmes on September 12 2006 at 11:35pm
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