Laist kindly sums it up "It’s a fact that all water has a certain amount of air dissolved in it, albeit invisible to the naked eye- most of the time. But, there are times when the temperature of the water in the underground pipes is much lower than the comfortable temperature inside our homes and workplaces. At times like these, the dissolved air in the water shows up when you turn on the tap. What the eye sees as cloudy, even milky, water is actually undissolved air escaping in the form of bubbles. "
It's safe to drink, clean and wash with just like usual even though it looks really freaky.
