system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Doesn't water need to be over 100 degrees celsius to become steam? Why is there water vapour in our hot showers?
gpt
The simple explanation:

Water *boils* at 100 Centigrade. That's the temperature at which it is *definitely* becoming a gas. However —

Water molecules can, and do, get enough thermal energy to pop off the surface of water *all the time*, no matter *what* temperature the water mass is at. It even happens with ice! You can have a block of ice sitting in a mass of dry air, and water molecules will pop off the surface into the air. This is titled *sublimation*.

This all happens because the deciding factor of whether water molecules pop off the surface of a mass of water is determined by the *vapour pressure* — a comparison of how energetically the molecule wants to pop off versus how capable the surrounding space is to allowing that.

Ice, even at ridiculously low temperatures, still has some vapour pressure — it's just much lower than the atmosphere around it.

Water, at room temperature, even at 35°C, has a vapour pressure roughly equal to the surrounding room-temperature air, or a somewhat more. This can lead to humid shower rooms and fogged mirrors.

When you push the warm water through a showerhead, though, you're applying a *very* large amount of kinetic energy to the molecules and *greatly* increasing the surface are of the mass of water.

This *skyrockets* the vapor pressure on the surface of the water streams, causing a huge push of vapour into the atmosphere, saturating it.