Have a strange question here;

I used to freeze ordinary tap water for making my ice cubes, a few weeks ago I started freezing store bought Mineral water for my ice cubes (well known and expensive brand), however as the ice cubes melt in the water, they leave behind a white powdery substance in the bottom of the glass. I suspected this may be just the Minerals that are present in water like calcium etc. but I'd like to know for certain, and is it safe to swallow ?

Thanks.

This link may shed some light on it.

Is it normal to have white flakes in ice cubes or hot water? (http://www.querycat.com/faq/ce8ecd58a2eae694bb8ff934db36c657)