Difference between revisions of "Water purification"
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Methods that are '''not''' effective at removing viruses: | Methods that are '''not''' effective at removing viruses: | ||
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== Purification methods == | == Purification methods == | ||
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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.<ref name="cdc"/> | 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.<ref name="cdc"/> | ||
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| + | === Filtration === | ||
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| + | 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. | ||
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| + | Viruses are too small to be blocked by any physical filter. '''Filtering is not effective against viruses''', unless the filtration device utilizes some additional means of disinfection (e.g. a chemical matrix) to kill viruses. | ||
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| + | Main article: [[Water filtration]] | ||
Revision as of 01:16, 3 April 2017
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water.[1]
Contents
Contaminants
Aside from sediment, contaminants typically found in non-purified water are[2]:
- Protozoa
- Bacteria
- E. coli
- Salmonella
- Campylobacter
- Shigella
- (many others)
- Viruses
- Hepatitis A
- Enterovirus
- Norovirus
- Rotavirus
- (many others)
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:
- Gastrointestinal illness (for example, diarrhea, vomiting, cramps), hepatitis, meningitis.
Sources of viruses in drinking water are:
- Human and animal fecal waste.
Methods that are effective at removing viruses:
- Boiling (Rolling boil for 1 minute minimum) - very high effectiveness;
- Disinfection with iodine, chlorine, or chlorine dioxide - high effectiveness;
Methods that are not effective at removing viruses:
- Filtration - not effective;
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. Filtering 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
