Water treatment

Water is the most common compound on Earth, its physical-chemical features makes it unique (dielectric constants, density, boiling and melting point). In its natural state, and depending on the ground, it contains some impurities in major or minor degree. It is necessary, then, to treat it before or after use, as to:
Meet human consumption regulations.
Meet the requests of the processes in which it is going to be used.
Meet disposal regulations.