Water Purification

• Water treatment is usually meant to produce water that can be safely consumed by people or livestock, although it may sometimes produce water for other purposes, such as a particular industrial process. Purification options may be roughly divided into four main types: physical, chemical, biological and radiation. Each has its own advantages and disadvantages and is best suited to a particular situation.
  
  

Physical Purification

• The simplest method of physical purification is filtration. Coarse filters can be used to remove silt and other objectionable physical contamination. Much finer filters, called membranes, can also remove microbes and germs, although some filters may not remove smaller viruses. Even fine membranes won't remove dissolved chemical contamination; but a process known as reverse osmosis can remove chemicals such as dissolved salt by forcing water through a special membrane. Activated carbon filtration is a complementary method that will remove dissolved chemicals. Simply boiling water is another physical technique that will kill most microbes, but won't remove chemicals.
  
  

Chemical Purification

• Chemical purification is generally only helpful in removing biological contamination --- microbes such as bacteria and protozoa that can cause disease. This technique simply involves adding a chemical to water in sufficient concentrations that it kills the microbes. Common chemical purifiers include chlorine, chloramine, iodine and ozone. Some of these chemicals, such as chlorine, have the added advantage of remaining in the water and continuing to kill microbes long after the chemical is added. One drawback is that some chlorine-based compounds are known to react with organic material in water to form small quantities of cancer causing chemicals.
  
  

Biological Purification

• A common method of biological purification which requires no external energy source is slow sand filtration. In this technique, water to be treated is slowly drained through a bed of sand on which a thin layer of organic matter has been allowed to grow. This organic layer --- or biofilm --- contains helpful bacteria, insect larvae, fungi and other living things. As the water slowly trickles through this layer, physical and biological contaminants are filtered out and digested by the various organisms in the biofilm.
  
  

Radiation Purification

• Ultraviolet (UV) radiation is capable of affecting many microbes, such as bacteria, so they can no longer reproduce. Since UV light systems are inexpensive, portable and easy to use, there are advantages to this method. Disadvantages are that the UV light will not penetrate well into murky or turbid water. As well, some microbes are less susceptible than others and may even recover from UV exposure.