Water purification

Background

Water purification is critical in certain settings to minimize waterborne diseases. This is especially true for international travelers, military personnel, and anyone living in area with potentially contaminated water sources. Natural water can become contaminated through a myriad of ways including, but not limited to: organic or inorganic material from land erosion, dissolution of minerals, decay of organic vegetation, biologic organisms that reside in soil and water, industrial chemical pollutants, and microorganisms from animal or human biologic waste.

This article discuss the benefits good hygiene and adequate sanitation as well as provide ways to treat water for safe drinking.

Benefits of Water Purification

The World Health Organization (WHO) reports that 780 million people still lack access to clean water supply. This does not include military personnel, individuals providing aid in 3rd world countries, or even people on wilderness adventures.

  • Primary reason for water treatment is to prevent gastrointestinal illness from fecal pollution with enteric pathogens.
  • Appearance, odor, and taste are not reliable to estimate water safety.
  • Treating water provides enormous benefits with minimal risk.
  • Treated water, hygiene, and adequate sanitation ability to reduce diarrhea and other diseases is well documented.
  • 94% of diarrheal cases globally are preventable.

Waterborne Enteric Pathogens

Disinfection Methods

  • Heat - perhaps the oldest and most efficacious method
    • Advantages
      • Does not impart additional taste or color to water
      • Single-step process that inactivates all enteric pathogens
      • Efficacy is not compromised by contaminants or particles in the water, as with chemical treatment and filtration
      • Can pasteurize water without sustained boiling
    • Disadvantages
      • does not improve taste, smell, or appearance of poor-quality water
      • Fuel sources may be scarce, expensive, or unavailable
      • Does not prevent recontamination during storage
    • Boiling
      • Evidence indicates that enteric pathogens are killed within seconds by boiling water.
      • Water brought to a boil should be adequately disinfected.
      • Extra margin of safety can be added by boiling for 1 minute or by keeping the water covered for several more minutes, which will maintain high pasteurization temperature without using fuel, or allowing it to cool slowly. Although the boiling point decreases with increasing altitude, this is not significant compared with the time required for thermal death at these temperatures.
    • Hot Tap Water
      • As a rule of thumb, water too hot to touch falls within the pasteurization range.
      • Tolerance to touch can vary reducing reliability
      • Water sitting in a tank near 55° to 60° C (131° to 140° F) for a prolonged period, enteric pathogens will be significantly reduced, likely to potable levels.
  • Physical Removal
    • Filtration
      • Advantages
        • Simple to operate
        • Mechanical filters require no holding time for treatment (water is treated as it comes out of filter)
        • Large choice of commercial products
        • Adds no unpleasant taste and usually improves taste and appearance of water
        • Rationally combined with halogens for removal or destruction of all pathogenic waterborne microbes
        • Different pore sizes available determine removal of microorganisms and smaller substances, including sodium (salt)
        • Effectiveness not dependent on water temperature
      • Disadvantages
        • Adds bulk and weight to baggage
        • Most filters not reliable for adequate removal of viruses
        • Expensive relative to chemical treatment
        • Channeling of water or high pressure can force microorganisms through the filter.
        • Eventually, clog from suspended particulate matter; may require some maintenance or repair in field
        • Smallest pore sizes (nanofilters, as in reverse osmosis) require higher pressure.
        • Freezing water within filter element will compromise or destroy some filters.
    • Adsorption
      • Charcoal, clay, and other types of organic matter (activated [burnt] coconut shell)
      • Usually used in combination with filtration
  • Chemical Disinfectants (Halogens) - most widely used form worldwide
    • Chlorine
    • Iodine
    • Chlorine vs Iodine
      • Iodine has lower oxidation potential, reacts less readily with organic compounds, is less soluble, is less hydrolyzed by water, and is less affected by pH, all of which indicate that low iodine residuals should be more stable and persistent than corresponding concentrations of chlorine. The major disadvantage of Iodine is concern for its physiologic activity.
  • Misc Disinfectants
    • Ultraviolet Light - SODIS method widely and easily implemented
      • Advantages
        • Effective against all microorganisms
        • Imparts no taste
        • Some portable devices now available commercially
        • Can use UV rays from sunlight in austere conditions
      • Disadvantages
        • Requires clear water
        • Does not improve water esthetics
        • No residual effect; does not prevent recontamination during storage
        • UV lamps are expensive and require power source.

See Also

External Links

References

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