A system and a method for reusing waste water from a Reverse Osmosis (RO) filtering process are described, said system including: a Reverse Osmosis (RO) filtration system, from which a flow of highly alkaline waste water results; two tanks intended to receive waste water and able to alternately determine the physical and chemical properties of waste water through sensors or, and perform homogenization, chlorination and chemical treatments of said waste water; an output line which comprises a pump and connects the tanks to a reservoir; and said reservoir being able to blend the water treated by the tanks with treated chlorinated drinking water, depending on the physical and chemical properties of these volumes of water; the chlorination and chemical treatment includes addition of a hypochlorite compound, which reaction releases chlorine in the waste water and causes evaporation of at least O2 and H2 gases, reducing the alkaline pH of said waste water.