ACTIVATED CARBON WATER FILTERS
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
- 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
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
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.
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.
Osmosis Water Filters
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