Water starts evaporating at anything above zero Celsius at sea level and 1 atmosphere of pressure: this is because evaporation is diffusion of molecules due to differences in pressure and concentration, not just boiling. Heat speeds up the process, but is not the primary force behind this.

Because boiling isn't evaporating. Water boils at 100 C but can evaporate at any temperature above 0 C.

The temperature of some amount of water is basically the average kinetic energy of its molecules. Some molecules will have more energy and some less.

Some of the molecules with more energy will be at the surface.

And some of those high-energy surface molecules will have enough energy to overcome the surface tension of the water and pressure of the air above it and shoot off into the air.

This is evaporation.

So, over time, any body of non-frozen water will slowly evaporate.

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The thing that's missing is water evaporates due to heat energy, not boiling. Boiling makes water evaporate quickly, but water can evaporate near its freezing point just more slowly.

Liquid water evaporates at all temperatures, so puddles disappear because they evaporate. The evaporation is somewhat faster with higher temperatures and slower with lower temperatures. Evaporation happens from the open surface of water. The larger the surface, the faster the evaporation. For this reason a puddle evaporates faster than the same volume of water in a glass. Boiling, however, happens throughout the entire volume of water at the same time, and is therefore much faster than simple evaporation.

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Evaporation, in ELI5 terms, is simply a molecule of water getting so excited that it literally jumps out of the container in which it is stored.

A puddle of water contains a bunch of water molecules which are all bouncing against each other and their container, but they don't have the energy needed to actually bounce out of the container. Then a (relatively) warm room or a little bit of sunlight provides some extra energy, and a molecule gains the extra energy needed to leap out of the puddle and into the air.

This can happen at any temperature above O C.

At temperatures below 0 C, as described in other posts, water molecules can skip the liquid phase and go straight from ice to vapor in a process called sublimation.

It all boils down (pun absolutely intended) to energy input.

Water is just a bunch of molecules.

Imagine you have two friends who are identical twins (hydrogen atoms). You (an oxygen atom) stand between them and hold one of each of their hands (you are now a water molecule). You guys do everything together, and sometimes you’re tired and fall asleep, and sometimes you’re really active and running around like crazy, but you’re always holding hands. Now imagine there were millions , and millions of people exactly like you, all holding hands with identical twins - you’re all going about your lives, sometimes moving fast, sometimes moving slow. When it’s cold, like in winter – you’re more likely to stay at home, hang out with your friends inside, and not really do much. In the summer when it’s really warm outside, you guys are more energetic, and it’s way more likely that you go too far and too fast and lose track of the pack.

Imagine that you three, and a whole bunch of people exactly like you (other water molecules) were hanging out in a really big group, sometimes the threesomes that are moving really, really fast, and are on the edges of the group - lose track of everybody else, and end up separated. They just go off and do their own thing while the group continues on hanging out together.

That is exactly what happens with water. When water gets warmer, more “threesomes” are out running around and moving faster, therefore more of those “threesomes”, a.k.a. molecules get separated from the group, i.e. evaporate.

Now, when water gets to 100°C, it’s like every threesome in the group started moving that fast, and that energetically, that they are all equally likely to get separated and get lost - no Matter where in the group they are located – the group gets spread out further and further apart because everybody is running around so fast.

Basically, when a molecule leaves the pack – it evaporates. When every molecule in the pack is moving so fast that they are all equally likely to get separated, that is “boiling”. For water, that happens at 100°C.

TLDR: Ten wild monkeys alone in a room with a big pile of Legos on a pillar will make a mess a lot faster than if the pile of Legos laid in a pit.

Evaporation: The molecules that the water is made of constantly bump into each other, sometimes these molecules get unlucky and get punched so hard, that they are thrown out into the air. Most don't get very far, however, since they run into the air molecules, which kindly kick them back into the water. Still, if the molecules get far enough away, the can catch a breeze and escape.

Boiling: The molecules in the water are much more violent at high temperatures. At some point, a hole with no molecules will form in the water. Since the molecules mosh so violently into this pit, they end up slamming into the sides of the pit violently enough, that it expands despite of the rest of the water pushing back. That is how bubbles form. The bubbles then rise to the surface, and push the air away with their energy and numbers.