In the seventh century, Thales believed that water vapor from the oceans was pushed up into space by wind. Outside, people did not know the source of groundwater. They think that the water of the ocean comes from the force of the wind. In the 18th century, Erin Dylates, the great thinker, explained the theory of the water cycle. In the thick clouds and become what is called a mountain of clouds that can hold a huge amount of millions of cubic meters of water. During the rainy season, when the thick clouds touch the cold wind, millions of meters of water fall to the earth's surface. Al-Quran also mentions the cycle of water or the source of water on the planet. In the 21st sentence, Chapter 39 states and means in Khmer: "Have you not seen? Indeed, Allah sent down rain from the sky, and He brought it into the earth as a fountain of water. َمْلَمْ تَرَ أَنَّ اللَّهَ أَنزَلَ مِنَ السَّمَاءِ مَاءً فَسَلَكَهُ يَنَابِيعَ فِي الْأَرْضِ ثُمَّ يُخْرِجُ بِهِ مُّخْتَا مُّخْتَلِفًا أَلْوَانُهُ ثُمَّ يَهِيجُ هُاهُ مُصْفَرًّا ثُمَّ ُهُلُهُ حُطَامًا ۚ إِنَّ فِي ِكَلِكَ لَذِكْرَىٰلِأُو الْأَل