Water supply companies maintain a low level of chlorine in mains water to inhibit bacterial growth in the distribution network. Chlorine and naturally-occurring organic materials create a taste and smell that many people dislike.
Plumbed-in activated carbon filters work on the same principle as the jug filter to remove chlorine and organic substances but are not so effective on inorganics such as salts and metals. They consist of a filter head for connection to the water supply with a detachable bowl housing a filter cartridge incorporating a mechanical filter, which excludes grit, dirt, sand and so on.
The effectiveness of an activated carbon filter can be extended through additions to the basic filter material and different types of cartridge are now available, capable of removing or reducing a variety of additional substances. Activated carbon filters are also often used as the main element of a larger combination filter system, capable of removing heavy metals and nitrates.
Bacterial growth can occur in filters if they are left unused for a long period of time, as they would be, for instance, at a holiday home. To reduce potential bacterial problems, some activated carbon filters are impregnated with silver, which is known to inhibit bacterial growth. Any treated water not used immediately should be refrigerated.
All filter cartridges should be changed regularly, in accordance with the manufacturer's instructions. The maximum filter cartridge life recommended by BRITISH WATER is 6 months for standard filters and 12 months for those containing silver.