Activated Carbon

The basis of all water filters is a substance called 'Activated Carbon'. Activated carbon is derived from either coconut fibre or coal which is treated (or 'Activated') by being subjected to extreme temperatures and steam in the absence of oxygen.

This process produces an extremely porous material which can either be in a loose 'granular' form or a compressed tube commonly called a 'Carbon Block'. Loose granulated carbon is generally less hygienic than a tightly bonded block cartridge.

The quality, density and source of the carbon used in different GAC (Granulated Activated Carbon) or a Carbon Block cartridges varies enormously and effects the final performance.

Cheaper cartridges will improve the flavour of the water, but the better cartridges will remove a wider range of chemicals as well as THM's, and aluminium sulphate.

Better quality Activated Carbon Cartridges have additional technology, such as:

  • KDF - Standard Activated Carbon filters are not effective in removing the full range of potential 'Heavy Metals' from water. To remove metals, you will need a cartridge which includes a material called KDF. KDF also increases the hygienic life of a carbon cartridge by up to three years, because it helps to prevent the growth of bacteria within the cartridge. KDF should not be used for untreated bore or roof water supplies. It should also be noted that because the KDF media exchanges Chlorine & Metal ions for Zinc ions, there can sometimes be a very slight bitter taste caused by the output of the zinc. A standard Carbon Block cartridge therefore tends to produce a slightly sweeter taste.
  • Actival - Natural minerals, including fluoride will not be removed by either carbon or KDF purifiers. To remove added 'Sodium Fluoride' either use a cartridge with 'Actival', (a fluoride specific resin), or Reverse Osmosis.
  • Bacteriostatic - Some carbon filters claim to be "bacteriostatic". This does not mean they remove or kill bacteria; they simply contain a chemical, usually silver, to limit bacterial growth.
  • Pre-filters - are often used to remove sediment so that the filter works better and doesn't clog quickly.
  • Ion exchange - These filters contain resins which attract either positively charged or negatively charged chemicals.


Life of Filter Cartridge

The hygienic life of carbon cartridges varies from 6 months to 2 years depending on the manufacturing process and the source of the Activated Carbon. Some cartridges have silver bonded with the carbon to increase the hygienic life, as silver is a natural media which restricts many bacteria frombreeding.


Selecting A Water Filter Cartridge

To avoid infection with Giardia or Cryptosporidium cysts choose a cartridge with a 1 micron or less filter.

Limitations of Activated Carbon Filters

Untreated Water - Activated carbon can't remove disease-causing organisms (pathogens). They should be used only on water which has already been treated to make it safe.

Overused Cartridges - If the cartridge is not changed regularly, you may end up contaminating the water. Each time the filter is used some water remains in the carbon. Any bacteria in the water will also remain, along with organic substances that get trapped in the filter. Because there is no chlorine left to kill the bacteria, they can grow and multiply, feeding off the trapped organic material. Eventually they emerge in the water from your filter.

Write the installation date or expiry date on the cartridge before installing it. Some cartridges have an automatic shut-off or a reduction in flow upon expiry. For filters which don't provide such a warning, the standards require that the cartridge removes contaminants for twice the claimed capacity.

Carbon filter Performance - Some grades of carbon will remove impurities such as chlorine by-products (trihalomethanes, or THMs), herbicides, pesticides and other organic chemical compounds. But most just make water taste and smell better.

Cartridge Design - may allow water to stream through too quickly. The longer water is in contact with the surface of the filter material, the more chance there is for chemicals to stick to it.

Carbon particle size - the smaller the particle, the more outside surface area is available to attract impurities. Check your filter complies with an ccepted standard, such as the US National Sanitation Foundation (NSF) standard.


Filter Standards

Always buy a filter which complies with either NSF standard 53 (Health Effects) or the New Zealand water filter standard AS/NZS 4348. The label should list clearly what it will remove.

Next: Reverse Osmosis Water Filters

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