I've seen this with the aerator on the kitchen sink in several instances. Simply speaking the faucet causes a lot of tiny bubbles into the water. (Never have understood the purpose.) If you pour a glass, it will initially look somewhat chalky in color. If you let it sit for just a minute, all the tiny microscopic bubbles drift out and the water is again crystal clear.
Of course if it doesn't clear in a few seconds or it clears and you see settlement in the bottom of the glass, then that's a whole other story.
