Abstract: Disclosed is a process and apparatus for purifying a low polluted water containing concurrently or selectively inadequate matters including heavy metals such as iron contents and manganese, and fine suspended matters, which comprises adding a reactant primarily containing a colloidal silica from a reactant charger to the polluted water stored in a primary tank to emulsify the inadequate matters; adding a coagulant primarily containing chitosan into the polluted water from a coagulant charger; feeding external air under high pressure by a pump into the polluted water, and separating the air from the polluted water, followed by dissolution of the air under pressure in the polluted water using a water separator; injecting the thus treated polluted water into a polluted water stored preliminarily in a secondary tank to generate very fine bubbles in polluted water stored in the secondary tank under releasing of the pressure; allowing the inadequate matters emulsified and flocculated to float up onto the water surf