Here's why:

* Evaporation: This is the process where liquid water absorbs heat energy and changes into water vapor (a gas). This occurs at the surface of the liquid, and the rate of evaporation depends on factors like temperature, humidity, and wind.

Let's look at the other options:

* Condensation: This is the opposite of evaporation, where water vapor in the air cools and changes back into liquid water (forming clouds, dew, etc.).

* Freezing: This is the process where liquid water changes into solid ice.

* Melting: This is the process where solid ice changes into liquid water.

Therefore, evaporation is the only process that directly transforms liquid water into vapor.