Table 7

Determinand Point of Use Device Type and Efficiency  
  Activated Carbon
Filtration (plain)
Ion Exchange
Reverse Osmosis
Ultra Filtration
Ultra Violet
Calcium Filtration
Chlorine Dosage Magnetic Treatment
Arsenic (11) P N N-G N-G N-G Ex N-G N P-G N N
Bacteria N(1) Ex(4) G P P-M Ex Ex Ex(8) P Ex N
Boron N N N N Ex N N N N N N
Carbon Dioxide P G N N P P N N G N N
Colour M N N N P G P-M N N N-P N
Hardness P M(5) N N G(6) M P-M N N N P
Iron, soluble P N N N G(6) G M N M N-G(11) P
Manganese, soluble P N N N G(6) G M N M N-G(11) P
Nitrate, nitrite P N N N G(6) G P N N N N
Protozoa G(2) Ex(4) Ex G(2) N Ex Ex P(8) P(10) N-G(12) N
Tastes and odour G(3) M N N P M P N P N-M N
Turbidity M N P P G Ex Ex N P N N
Viruses M Ex(4) P P M Ex Ex Ex(8) P Ex N
Terms used in table:
Ex - excellent removal, where equipment is in good condition
G - good removal to an acceptable level
M - moderate removal, constituent may still give a problem
P - poor performance, most of constituent levels unaffected
N - no removal at all

Explanation of notes:

  1. Activated carbon filters should not be exposed directly to water containing biological contaminants; carbon granules can act as a growth medium for bacteria.
  2. Either plain or activated carbon cartridge type filters can remove protozoan cysts, as long as the nominal particle retention size of the filter is 1 micron or less; however, see note 1.
  3. Activated carbon will eventually become full of contaminants and must be replaced to prevent contaminants returning to the water.
  4. Boil water to a rolling boil for at least one minute.
  5. Boiling hard water removes some of the hardness, but a scale will form on the jug element making the element less efficient and shortening its life.
  6. UIon exchangers can remove a range of chemical contaminants if the appropriate resins are chosen. General purpose resins are often not suitable. Water softeners tend to just reduce the calcium content.
  7. While some treatment methods work well for some contaminants, they can be upset by the presence of others. For example, ion exchange, reverse osmosis and ultrafiltration are capable of removing a range of contaminants. When fouled with excess turbidity and bacterial growths, their performance falls off dramatically and they can break down.
  8. Ultraviolet disinfection is upset by anything that shields biological contaminants from ultraviolet light. This includes dissolved organic matter, which absorbs UV light, iron and manganese, lime scale, colour and turbidity. Keep these constituents low or remove them before using the UV device. The lamp must be kept clean.
  9. This treatment uses the form of calcium in calcium carbonate, marble or dolomite.
  10. This treatment is of variable effectiveness, depending on the exact details of the filter.
  11. Chlorine can oxidise soluble iron and manganese, which may then be removed by filtration. 
  12. A high dose/long retention time can inactivate Giardia; however, Cryptosporidium is unaffected.

Additional comments:

  • It is important to adhere rigidly to the manufacturer's operating and maintenance instructions. Operating filtration or adsorption equipment at high flow rates or switching suddenly from off to on can dislodge material that has previously been removed from the water.
  • Some people have found that magnetic treatment can modify the nature of sludges, from scale- forming to flocculent particles.
  • Cyanobacteria can produce cyanotoxins and these can have serious health effects. Activated carbon and reverse osmosis are able to remove cyanotoxins from water, but it would be preferable to avoid abstracting water during cyanobacterial blooms.
  • Pesticides in shallow bore water can be removed by activated carbon. If using roof water, isolate the storage tank while pesticides are being sprayed and do not reconnect until after rain.
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