The sun's heating water starts the water cycle. The water is evaporated and the molecules rise until cooled. The cooling water vapor makes clouds. The clouds continue to gather water vapors until they can no longer hold water. It begins to rain. The rain fills lakes, streams, rivers and oceans. The rain continues until the clouds are drained. They begin to decrease as the air warms up. The sun comes out and the cycle starts all over again. Without the sun's rays, the water cycle could never begin.