Water purification

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Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water.[1]


Contaminants

Aside from sediment, contaminants typically found in non-purified water are[2]:


Cryptosporidium

Potential health effects from ingestion of water contaminated with Cryptosporidium are:

  • Gastrointestinal illness (for example, diarrhea, vomiting, cramps).

Sources of Cryptosporidium in drinking water are:

  • Human and animal fecal waste.

Methods that are effective in removing Cryptosporidium from water are:

  • Boiling (rolling boil for 1 minute) - very high effectiveness;
  • Filtration - high effectiveness when using an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated "cyst reduction / removal" filter);

Methods that are not sufficiently effective in removing Cryptosporidium:

  • Disinfection with iodine or chlorine - not effective;
  • Disinfection with chlorine dioxide - low to moderate effectiveness;

Combination filtration and disinfection has a very high effectiveness in removing and killing Cryptosporidium when used with chlorine dioxide and an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated "cyst reduction / removal" filter).


Giardia lamblia

Also known as Giardia intestinalis.

Potential health effects from ingestion of water contaminated with Giardia are:

  • Gastrointestinal illness (for example, diarrhea, vomiting, cramps).

Sources of Giardia in drinking water are:

  • Human and animal fecal waste.

Methods that are effective in removing Giardia:

  • Boiling (rolling boil for 1 minute) - very high effectiveness;
  • Disinfection with chlorine dioxide - high effectiveness;
  • Filtration- high effectiveness when using an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated "cyst reduction / removal" filter);

Methods that are not sufficiently effective in removing Giardia:

  • Disinfection with iodine or chlorine - low to moderate effectiveness;

Combination filtration and disinfection has a very high effectiveness in removing and killing Giardia when used with chlorine dioxide and an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated "cyst reduction / removal" filter).


Bacteria

Potential health effects from ingestion of water contaminated with bacteria are:

  • Gastrointestinal illness (for example, diarrhea, vomiting, cramps).

Sources of bacteria in drinking water are:

  • Human and animal fecal waste.

Methods that are effective in removing bacteria:

  • Boiling (rolling boil for 1 minute) - very high effectiveness;
  • Disinfection with iodine or chlorine - high effectiveness;
  • Disinfection with chlorine dioxide - high effectiveness;
  • Filtration - moderate effectiveness when using an absolute less than or equal to 0.3 micron filter;

Combination filtration and disinfection has a very high effectiveness in removing and killing bacteria when used with iodine, chlorine, or chlorine dioxide and an absolute less than or equal to 0.3 micron filter (NSF Standard 53 or 58 rated "cyst reduction / removal" filter).

Viruses

Potential health effects from ingestion of water contaminated with viruses are:

Sources of viruses in drinking water are:

  • Human and animal fecal waste.

Methods that are effective at removing viruses:

Methods that are not effective at removing viruses:


Purification methods

Boiling

Boiling is the single most effective method of removing any active biological contaminants. Boiling water long enough removes all microorganisms and viruses from it.

To ensure full effectiveness, water should be brought to a rolling boil for at least 1 minute at normal elevations. However, because boiling temperature decreases with elevation, longer boiling times are required at high elevations. At altitudes greater than 6,562 feet (greater than 2000 meters), you should boil water for 3 minutes.[2]

Filtration

A water filter removes impurities by means of a sufficiently fine physical barrier. In order for a particular threat to be removed, pores in the barrier must be too small for it to pass. All filters can remove sediment, but sub-micron pore sizes are required to reliably remove microorganisms. Protozoa can get as small as 50 microns, and bacteria as small as 0.2 microns; thus, a 0.2 micron filter is required to reliably block them.

Viruses are too small to be blocked by any physical filter. Filtration is not effective against viruses, unless the filtration device utilizes some additional means of disinfection (e.g. a chemical matrix) to kill viruses.

Main article: Water filtration

Chemical disinfection

Exposure to certain chemicals, such as iodine, chlorine, or chlorine dioxide, can kill some or all microorganisms. The effect of these chemicals varies significantly - not all are effective against all threats. The amount of time necessary to fully disinfect water depends on the quantity of the chemical used, water temperature (cold water takes longer), and water clarity.

Iodine

Iodine reliably kills viruses and most protozoa. However, it is not sufficiently effective against Giardia.

In clear warm water, iodine takes ~30 minutes to perform at maximum effectiveness. If water is cold or turbid, considerably longer reaction time is required.

Iodine remains in the water after purification, negatively affecting its taste. Adding vitamin C to the water (after disinfection is complete) helps to precipitate most of the iodine still in the water, and makes the taste more subdued.[3].

Chlorine

Chlorine dioxide

Ultraviolet disinfection

Sufficiently long exposure to ultraviolet (UV) light will kill some microorganisms. Because the amount of exposure depends on water clarity, is it important to filter out all sediment to maximize the effect.

References

  1. https://en.wikipedia.org/wiki/Water_purification
  2. 2.0 2.1 A Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use
  3. https://en.wikipedia.org/wiki/Portable_water_purification