Book 30, Question 103
Why does tap water sometimes look milky and then clear up?
Sometimes water from the tap looks milky or cloudy when you first fill a glass.
The cloud is made of lots of tiny air bubbles. Water in pipes is under pressure, which keeps extra air dissolved in it. When it comes out and the pressure drops, the air forms bubbles, like in a soda. The glass clears from the bottom up, as the bubbles rise and pop. Milky water is safe.