Water cycle is like a simple distillation process. In laboratory, the heat source heats the water in a glass vessel. Water evaporates and travel through a cooled condenser tube. Cold passage turns the vapor to water droplets falling down to collection jar. The end is a cleaner water. Far cleaner than it was before.
In wider environment. Water from soil, plants, spring, rivers, seas and ocean evaporates due to heat and perhaps wind too. Vapors join together and form clouds. It become heavier as atmospheric water accumulate. Eventually condense and fall as rain.
Then rain is cleaner. I can be a source of safe drinking water.
My claim is barely true however!
The condensation is an open system. Water droplets on its journey may absorb dirt, microbes and harmful gasses. Sulfur with rain create acid rain.
It came from Earth and will be back again. Likely to contain substances it previously have – from soil, spring, rivers, seas and oceans.
At homes, water maybe collected via roof water downspout. If stored, use for laundry, bath, cleaning, dish washing but not as drinking water.
In rainy countries, building a mechanism to aseptically collect rain as potable water source is unlikely. It is collected using large dams, then treated and filtered before delivering to communities.