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The Soft Machine: Travel Health column

By CARRIE BEALLOR (continued from previous page)

Reverse osmosis uses high pressure to force water through a semi-permeable membrane. It filters out dissolved ions, molecules and solids, including salt from saltwater. It does remove viruses but this technology is quite costly and not commonly available commercially.
Where mistakes are made:

  • Drinking disinfected water with dirty hands or contaminated containers.
  • Drinking clean water while eating contaminated food.
  • Adding unsafe water to an alcoholic beverage. Wine and beer are generally considered safe, especially if straight from the can or bottle.
  • Drinking from a can or bottle without wiping the surface clean. Many contaminated hands may have touched the exterior.
  • Drinking beverages with contaminated ice. Ice is unsafe if made from unsafe water.
  • Drinking warm tea or coffee that was never brought to a boil. Hot drinks should be served piping hot and allowed to cool in your presence.
  • Drinking water accidentally during recreational activities such as swimming or water rafting. In questionable water, try to keep your mouth closed.
  • Brushing your teeth with unsafe water.
  • Drinking bottled water. Bottled water is perceived to be safe because it is packaged and the label often claims it has been treated, but in the developing world, the safety of bottled water can be questionable. Problems arise with the quality of disinfection used at the source, the packaging process and the hygiene of the workers, reusing bottles and false safety seals. Studies have found that bottled water sampled in some developing countries is indeed contaminated.

  • Activated charcoal can come inside a filter or in granules or powder. Pouring water through charcoal removes organic and inorganic substances by absorption and often improves the taste and smell of water. It does not kill micro-organisms. It can be used as a first step to remove chemicals which might interfere with halogen disinfection or as a second step to remove chemicals used to disinfect the water. An unpleasant taste, smell or discoloration may indicate that the charcoal is no longer active and should be replaced. A quick test with tinted water from food colouring can tell you the same -- the charcoal should remove the dye. If you accidentally ingest a few grains of activated charcoal it is generally not harmful.

    With sedimentation, turbid waters are left to settle, allowing larger particles to fall to the bottom and the cleaner top water to be poured off and then treated further if necessary. The time depends on the turbidity and content of the water but an hour would be a good first try.

    Coagulation-flocculation is a process where a chemical powder like alum or potash is added to turbid water. When the water is stirred, unwanted particles stick to the chemicals by electrostatic forces and can then be removed by sedimentation or filtration and the water further treated if necessary.

    Halogenation refers to ... story continued.