In the water cycle, evaporation occurs when sunlight warms the surface of the water. The heat from the sun makes the water molecules move faster and faster, until they move so fast they escape as a gas. Once evaporated, a molecule of water vapor spends about ten days in the air.

Why does water evaporate at room temperature?

At room temperature, there is evaporation (I wouldn't call it excitation). This is because there are a few molecules of water which can manage to muster enough energy to escape from the large body of molecules and escape into air.

Why does water evaporate when it's not boiling?

The heat in that water results in some molecules moving fast enough to escape into the air, that is, evaporate. No additional source of energy is required for evaporation, and the water does not need to reach the boiling point to evaporate. As we've seen, water will evaporate at room temperature.