METHODS OF WATER PURIFICATION
Filters:
Consist of plastic or ceramic material packed tightly together to form a fine mesh or screen that physically prevents foreign particles from the water passing through the filter. However, as the level of foreign particles builds up the filters become clogged and must be replaced with new filters. They should not be relied upon to remove micro-organisms from water.
Activated Carbon Filters:
Use highly porous, slightly positively charged, charcoal to adsorb gases such as chlorine and carbon based organic impurities (including many pesticides) which can improve the taste of water. However, carbon filters generally do not effectively remove many dissolved inorganic minerals and metallic salts. Frequent filter changes are necessary to prevent bacteriological contamination.
Reverse Osmosis (RO):
Produces pure water by forcing feed water under great pressure through very fine membrane filters whose mesh size is designed to allow only water molecules (which are smaller than the dissolved impurities) to pass through. The purity of RO water depends on water pressure, age and quality of the membrane. RO is generally suitable for removing most chemicals including metals, chlorides, fluoride, nitrates and pesticides but will not necessarily remove all odours from the water. RO is an expensive process which requires a lot of electrical power, wastes large amounts of water in backflushing and cleaning the membranes, and requires skilled monitoring and operation, regular servicing and frequent replacement of the membranes. RO is not suitable for processing sea water without expensive pre-filtering.
Solar Distillation:
Uses only the energy of the sun to vaporize water and produce high quality distilled, potable water. The Solar Water Purifier described in this web site uses only sunlight to convert most kinds of polluted water into pure, potable water.
Irradiation of water with germicidal ultraviolet light:
(commonly known as UV-C with wavelengths between 100 and 280 nm, where 1 nm is 10-9 metres or 10-6 cm) destroys the DNA bonds of living cells and eliminates their ability to multiply and cause disease. If used correctly, at sufficient intensity and for sufficient time (levels which depend on the clarity or turbidity of the liquid), UV-C can kill most bacteria and viruses. Most germicidal UV systems use low pressure mercury vapor lamps which produce an intense mercury resonance line at 253.7nm.
About 9% of the energy emitted by the Sun lies in the ultraviolet region (sub-divided into UV-C from 100 to 280 nm; UV-B from 280 to 315 nm and UV-A from 315 to 400 nm.) We are continually advised to minimise our exposure to the sun to avoid having our own body’s DNA affected by the solar UV, particularly UV-C.
Distillation:
Involves boiling water to produce steam and is the single most effective method of water purification. The boiled off vapour consists of molecules of pure water only, with all the previously dissolved minerals, suspended sediments, bacteria and viruses remaining behind in the un-vaporised liquid. When the pure water vapour strikes a cool surface it condenses and becomes distilled water.
Freshly distilled water often tastes "flat" because all the dissolved oxygen has been boiled off. After this water is allowed to cool and naturally regain some dissolved oxygen, the "flat" taste will disappear.
Vacuum Distillation:
Produces pure water at a lower temperature than the normal boiling point of 100ºC at sea level, by reducing the pressure above the water. If the atmospheric pressure is halved, then water will boil at 40ºC rather than 100ºC. However, vacuum distillation is an expensive process because it requires a lot of electrical power to produce the pressure reduction and to boil the water.
