Most towns water sources in the UK contain free chlorine to reduce the level of bacteria present in the water however this can add taste & odour and as a strong oxidant, can also attack water treatment medias such as ion exchange resin and reverse osmosis membranes. For these reasons, it is sometimes beneficial to remove the free chlorine.
Surface waters may similarly contain high levels of organics which can add an unpleasant colour to water and can also foul reverse osmosis membranes.
Activated Carbon (AC) is a specialised water filter media, primarily used for the reduction of chlorine and related contaminants from mains water supplies.
Activated Carbon is most often a coconut shell product treated with steam and pressure to create a media with an enormous number of porous sites in, and over, the entire surface; these sites being positively charged. As water passes across the carbon media, the contaminants are held within deep fissures, on the surface or are altered by the catalytic action of the media; backwashing subsequently cleaning the filter bed.
AC performance will vary depending on contact time; with extended contact time often being required for effective colouration & organic removal.