Water is a compound that is composed of hydrogen and oxygen atoms.
The chemical formula of water is .
Purest form of water:
The purest form of natural water is rainwater.
The purest form of natural water is deprived of any contaminants including salts/minerals/particles or chemicals.
In the case of the sun, the rainwater comes straight from the condensation of vapor.
The water evaporates from ponds/lakes/rivers. During the vaporization cycle, all the impurities are removed, and then water in the form of rain falls straight into the soil.
Such pure water can be achieved in laboratories by the method of distillation.