I'm not sure what it is. At first I thought maybe dissolved gas bubbles, sometimes my water is really full of tiny bubbles that look like that. But it usually clears off pretty quickly. I would guess, though, that after being filtered for a while it will clear up on it's own. Maybe try aging your tap water a few days before adding it and see what happens to it. Or maybe try running the water a while before using it, see if that makes a difference. Hardness, in and of itself, won't cause the water to be cloudy. But I guess there could be some chemical reaction going on or something.