Granular activated carbon is a highly porous adsorbent material, produced by heating organic matter, such as coal, wood and coconut shell, in the absence of air, which is then crushed into granules. Activated carbon is positively charged and therefore able to remove negative ions from the water such as ozone, chlorine, fluorides and dissolved organic solutes by absorption onto the activated carbon. The activated carbon must be replaced periodically as it may become saturated and unable to absorb. Activated carbon is not effective in removing heavy metals.

Activated carbon is often used as a filter in water treatment systems, where water is directed downwards through a stationary bed of activated carbon, leaving organic material to accumulate at the top of the bed...