natural activation 4 stage UF water purifier(water purifier,UF water purifier,water softener) natural activationThey are 4 stages.Stage 1: ... , selenium, iron, chromium, aluminum, nickel and copper, as well as to suppress thegrowth of bacteria and algae. Stage 3 ... bleaching agent, phenols, trihalomethanes and other carcinogenic substances as well as odor, foreign color and residual chlorine.Stage 4: ...