I noticed the same floating scum in my teas and just had to do something about it. I was especially upset seeing it develop in a Cuisinart electric kettle that I received over the holidays last year. The scum developed all over the inside of the kettle and it was difficult to clean out. I noticed that I didn't have problems using distilled water in my Nespresso machine and I thought that might be an option. One consideration however was that I am a prolific drinker of tea these days and thought it may not be great to be drinking Arrowhead distilled water throughout the day. After some thought I wound up trying SmartWater, which is distilled + electrolytes. I am having great success using the SmartWater in my kettle now, which has remained pristine inside (Yay!!) and the taste is perfect for the tea I make. I don't think there are any problems with using heated/boiled SmartWater from a health stand point. If anyone has feedback to the contrary, I'm all ears.