When I drink a glass of ice water I see little white flakes falling to the bottom of the glass, what are these

I believed that this was due to our freezer blowing dust or something in the water so I conducted a little experiment. I put two ice cube trays in a ziplock bag. One filled with tap water and one filled with bottled water (kroger). When the water froze I put the ice cubes in glasses of bottled water. Both glasses had the white flakes falling from the ice and settling on the bottom of the glass.