Evaporation and condensation are both phases that water goes through. By allowing the water to evaporate,it will go from a liquid state,to a gas state. Anything that is not water will stay behind. Meaning all impurities will not become a gas like the evaporated water. As the newly formed gas rises into the atmosphere,it will begin to cool down and condense into tiny water droplets. These droplets will then collect into a substantial amount of clean water,making it safe to drink.