United States Environmental Protection Agency
GRADE LEVEL: 4 – 7
BACKGROUND: The following demonstration illustrates how the water cycle helps to purify water.
The key terms are evaporation and condensation. Evaporation is defined as the process through which a
liquid becomes a vapor. Condensation is the process through which a vapor becomes a liquid, and is the
opposite of evaporation. In the case of water, the main mechanisms for evaporation and condensation are heating and cooling, respectively.