Why does steam look white?
Short answer
Water vapor itself is an invisible gas. What we see as white steam is made of tiny liquid water droplets that form when warm vapor cools in the surrounding air.
How it works
Near a kettle or a hot drink, water first becomes water vapor. As that vapor mixes with cooler air, some of it turns back into tiny liquid droplets. This change is called condensation.
The droplets scatter many colors of visible light in similar ways. Light from many droplets reaches our eyes, so the cloud looks white. A clear gap may appear right next to the heat source because the water is still an invisible gas there.
Key point
Visible steam is not smoke. However, material released by burning fuel can contain other gases or particles. Steam is also harder to see in warm, dry air because fewer droplets form.