It is quite hard to see evaporation. But here is a way of finding out how much water can evaporate into a classroom.

Get a dish with a wide top. Fill the dish with water until it almost spills over.

Come back to the dish in a week and pour water from a measuring jug into the dish until it is completely full again.

How much water did you have to pour in?

Did this amount surprise you?

Where did the water go?