There is water in the air! Some of the water in the air is little droplets of liquid water or ice crystals. Little drops or ice crystals make clouds. But much of the water in the air is invisible! It is a gas called water vapor.
To figure out how much water is in the air, scientists measure the humidity. Humidity can change each day where you live. Also, humidity is different in places on Earth that have different climates. Dry air in a desert has lower humidity than the sticky, humid air in a tropical rainforest. Warm air can hold more moisture in it than cold air.