Why is my drinking water cloudy?
Once in a while, you get a glass of water that looks "cloudy;" maybe "milky" is a better term. After a few seconds, it miraculously clears up! The cloudiness is likely due to tiny air bubbles in the water. Like any bubble, the air rises to the top of the water and goes into the air above, clearing up the water. Cloudy water is completely harmless.
This phenomenon is more common when it is cold outside, because cold water is able to hold more air. In the winter, water from the distribution main - which is very cold - warms up during its travel to your tap. Some of the air that was once dissolved is no longer soluble, and comes out of solution in the form of air bubbles.
Water pressure is another factor. In order for water to get to your tap, it is pressurized in the distribution system. Water under pressure holds more air than water that is not pressurized. Once the water comes out of your tap, the water is no longer under pressure, and the air comes out of solution as bubbles (similar to a carbonated soft drink).
The best thing to do with cloudy water is let it sit in an open container until the bubbles naturally disappear.