The milky or hazy appearance of heated tap water is frequently attributable to dissolved gases, most commonly air. Cold water holds more dissolved gases than warm water. When water is heated, these gases become less soluble and are released, forming microscopic bubbles that scatter light, thus creating a cloudy visual effect. Similar observation is seen in carbonated beverages when the container is opened; the sudden release of pressure allows dissolved carbon dioxide to escape, forming bubbles.
This phenomenon is typically harmless and poses no threat to potable water quality. Its occurrence indicates that water is adequately pressurized, which is a factor in efficient distribution within a plumbing system. Historically, the presence of air bubbles has been incorrectly associated with health concerns; however, modern water treatment and distribution infrastructure are designed to minimize potential contaminants, and the presence of air bubbles is not an indicator of such contaminants.
