Why would water appear cloudy in a glass and then clear up?

Dissolved air in the water can cause cloudiness that will disappear in a few minutes. Air can be dissolved in the water a variety of ways. Air can enter a water main during a repair and become dissolved in the water. When cold water from the water main enters a warm building, air escapes from the water and can make the water look cloudy or milky. The cloudiness usually occurs more often in winter than in summer because cold water can hold more dissolved air than warm water. Air can also be dissolved in the water from a faucet aerator causing the water to appear cloudy.  more