Table 6.1Drinking-water disinfection methods for use by travellers

MethodRecommendationWhat it doesWhat it does not do
BoilingBring water to a rolling boil and allow to coolKills all pathogens

Does not remove turbidity/cloudiness

Does not provide residual chemical disinfectant, such as chlorine, to protect against contamination

Chlorine compounds:
  1. Unscented household bleach (sodium hypochlorite)
  2. Sodium dichloroisocyanurate tablet
  3. Calcium hypochlorite

For typical room temperature and water temperature of 25 °C, minimum contact time should be 30 min; increase contact time for colder water—e.g. double time for each 10 °C less than 25 °C

Prepare according to instructions

Should be added to clear water or after settling or clarification to be most effective

Type and typical dosage:

  1. Household bleach (5%)—4 drops per litre
  2. Sodium dichloroisocyanurate—1 tablet (per package directions)
  3. Calcium hypochlorite (1% stock solution)a—4 drops per litre

Effective for killing most bacteria and viruses

Longer contact time required to kill Giardia cysts, especially when water is cold

Not effective against Cryptosporidium; not as effective as iodine when using turbid water
Flocculant-chlorine tablet or sachetDose per package directionsEffective for killing or removing most waterborne pathogens coagulant-flocculants partially remove Cryptosporidium)Flocculated water must be decanted into a clean container, preferably through a clean fabric filter
Iodine:
  1. Tincture of iodine (2% solution)
  2. Iodine (10% solution)
  3. Iodine tablet
  4. Iodinated (triiodide or pentaiodide) resin

25 °C—minimum contact for 30 min; increase contact time for colder water

Prepare according to package instructions

Type and typical dosage:

  1. Tincture of iodine (2% solution)—5 drops per litre
  2. Iodine (10% solution)—8 drops per litre
  3. Iodine tablet—1 or 2 tablets per litre
  4. Iodinated (triiodide or pentaiodide) resin—room temperature according to directions and stay within rated capacity
Caution: Not recommended for pregnant women, for people with thyroid problems or for more than a few months’ time. Excess iodine may be removed after iodine treatment through use of a carbon filter or other effective process.

Kills most pathogens

Longer contact time is required to kill Giardia cysts, especially when water is cold

Carbon filtration after an iodine resin will remove excess iodine from the water; replace the carbon filter regularly

Not effective against Cryptosporidium
Portable filtering devices:
  1. Ceramic filters
  2. Carbon filters; some carbon block filters will remove Cryptosporidium—only if tested and certified for oocyst removal
  3. Membrane filter (microfilter, ultrafilter, nanofilter and reverse osmosis) type devices
Check pore size rating and reported removal efficiencies for different pathogens (viruses, bacteria and protozoa) provided by manufacturer and certified by a national or international certification agency. Filter media pore size must be rated at 1 μm (absolute) or less. Note that water must be clear to prevent clogging of pores. Filtration or settling of turbid water to clarify it is recommended before disinfection with chlorine or iodine if water is not boiled

1 μm or less filter pore size will remove Giardia, Cryptosporidium and other protozoa

Approved reverse osmosis device can remove almost all pathogens Some filters include a chemical disinfectant such as iodine or chlorine to kill microbes; check for manufacturer’s claim and documentation from an independent national or international certification agency

Most bacteria and viruses will not be removed by filters with a pore size larger than 1 μm

Microfilters may not remove viruses, especially from clear waters; additional treatment such as chemical disinfection or boiling/pasteurization may be needed to reduce viruses

Most carbon block filters do not remove pathogens, other than possibly protozoa, even if carbon is impregnated with silver, because pore size is too large (> 1 μm)

a

To make a 1% stock solution of calcium hypochlorite, add (to 1 litre of water) 28 g if chlorine content is 35%, 15.4 g if chlorine content is 65% or 14.3 g if chlorine content is 70%.

From: 6, Application of the Guidelines in specific circumstances

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Guidelines for drinking-water quality: Fourth edition incorporating the first and second addenda [Internet].
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