The most likely culprit is dissolved air. Cold water holds more dissolved gas, but when it’s heated in your water heater, the air expands and forms tiny bubbles.
These bubbles scatter light, making the water appear milky white. It’s the same reason sea foam looks white: millions of microscopic air pockets reflecting all colors back at you.
Fun fact: this phenomenon happens faster with hard water, which contains more minerals that help trap air. So if you live in a region with hard water (hi, Midwest!), you’ll see this more often.
How to Test It (No Lab Coat Required)
Fill a clear glass with the cloudy hot water. Then wait thirty seconds—literally just stand there. As the water settles, the bubbles rise to the surface and pop.
If the water clears from the bottom up, it’s air. That’s the telltale sign. If it stays cloudy, you might have sediment or a plumbing issue—but that’s very rare with modern systems.
Pro tip: Run the tap for a few seconds before filling your glass. Aerated water often looks cloudier right at the start of a cycle.
