Rain is a natural phenomenon that is part of the process of purifying water. It is exactly like the process of water distillation in the laboratory.
The book 'Ilmi Tafsir with the theme of Water in the perspective of the Qur'an and Science explains, when yawning, water molecules fly away leaving their dissolved ingredients. Although among these solutes there is a gas (eg Co2, NOx, or methane) or a substance which can also turn into a gas phase (eg chlorine), evaporation will separate water from its impurities.
Therefore, rain water is basically pure water. This is as explained in one verse of the Qur'an.
He is the one who breathes the wind (as) the bearer of glad tidings up close before the coming of His mercy (rain); and We bring down from the sky a very clean water. Surah Al-Furqan Surah 48.
God has created rainwater in a clean state for various purposes of the beings and enriches the barren land. However, the action of some humans that resulted in pure, clean water became contaminated.
There are times when the act is not aware of its negative impact, either in the short or long term. Sometimes, it is conscious, though consciousness is overcome by greed.
Humans no longer care about the survival of creatures in nature that belong together, including those belonging to future generations. This warning has been spoken by God to man.
It appears that the damage on land and in the sea is caused by the deeds of the hands of men, that God may feel to them some of their (consequence) deeds, that they may return (to the right path). Surah Ar-Rum Surah 41.
The process of rain
The water on Earth undergoes evaporation. This happens because of the sun that heats water on Earth. Then, the moisture accumulates in the air and undergoes compaction (condensation).
The book 'Amazing !!! The Best Science Stories of the Qur'an 'explains that the result of this condensation is called the cloud. A gust of wind will move the cloud. As a result, clouds overlap and continue upward to a cooler temperature.
The pile of clouds in the sky is getting more and added with a gust of wind is getting louder, making the clouds become heavy. Then, clouds can not support water or ice contained in it.
Thus, down the grains of water or ice to the surface of the Earth (the process of precipitation). The longer the water droplets or the ice. It is called rain. If the temperature is very low, then the fall is snow, so called snowfall.