Travel Health Zone - Water purification

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Water purification

The following is a list of methods for obtaining clean, safe drinking water.

Bottled water
If you are not planning on going out into the wilderness then the option of buying bottled water is a good one. Widely available in most countries bottled water is a relatively cheap and easy source of safe drinking water. However you must make sure that the seal on the bottle is unbroken as it is not unknown for locals to refill empty bottles with tap water and try to sell them as new.

Boiling is an excellent way to make contaminated water safe to drink but takes a little time and requires the necessary equipment (i.e. some source of heat or fire). To boil water properly it should be kept at a vigorous, rolling boil for at least one minute and at high altitude for up to up to five minutes (at 5,800m [19,000ft] water boils at 178oC). The main draw back with boiled water is that it tastes flat; this can be overcome by vigorously shaking it in a container with an air gap for a minute or so, or by leaving the boiled water to stand in a partly covered container for several hours.


Filtering water can be a good way to purify contaminated water but its effectiveness varies with the quality of the filter. It is important that the filter you choose filters viruses as well as bacteria, so check before buying. There are several different types of filter on the market and can be divided into three main categories.

Gravity filters - slower, bigger and generally less effective, gravity filters work by allowing water to percolate down through an inner core, usually in the form of an iodine or charcoal impregnated element. Some are ridiculously slow and should only be considered as a backup or if you have plenty of time on your hands.

Hand-pumped filters - these are a great improvement on gravity filters and work by forcing water through a micro-porous ceramic filter, sometimes in conjunction with a chemical sterilisation element. This type of filter is ideal for motorcyclist, cyclists and backpackers. They are more expensive than gravity filters but provide safer drinking water at a much-increased rate of about 0.5-1 litre per minute. The ceramic cores need regular cleaning, especially when filtering heavily sedimented water (pre-filtering with a Milbanks bag [see below] will help reduce cleaning) but can last for 1,000's of litres.

Electric-pumped filters - if you are travelling overland using a larger vehicle it is worth considering and electric-pumped filter. They are wired into your vehicles battery and modern ones are activated by the drop in press caused by turning on the units tap. They draw little charge from the battery and save a lot of arm work and time. An inexpensive unit is available from Mantec in the UK.

Millbanks Bag - this useful piece of equipment is used to pre-filter heavily sedimented water and consists of a bag made from closely woven canvas. Developed for forces during World War II, using this bit of kit in conjunction with chemical sterilisation can make even the most heavily silted water safe and palatable to drink and will prolong the life of micro-porous ceramic filters if used as a pre-filter.

Treating with Chemicals

Treatment with chemicals is another efficient way to sterilise water but often gives the water a funny taste and can require up to two hours to take effect. If the water is heavily sedimented it will need pre-filtering using one of the methods outlined below.

Iodine - available in either tablets or crystals form, or as a tincture, iodine gives the water a slightly unpleasant taste, can be messy to use (stains clothing and skin) and is toxic in the event of overdose.
Note: As of October 2009, a new European Directive has removed Iodine from the list of approved chemical for use in treating drinking water.

Method of Water Purification Using Iodine Crystals
Dosage = 4 drops of 2% tincture per litre
  1. Make a saturated solution by roughly quarter filling a 20ml glass (eats through plastic at this strength) bottle
  2. Top up with water and shake vigorously until no more crystals appear to dissolve, allow to stand for at least half an hour, shake again, and then allow remaining crystals to settle
  3. Pour off 10ml (not the crystals) of solution into a litre bottle of water, shake and leave for 10 minutes.
  4. Top up 20ml glass bottle ready for next use, should last to purify about 1000 litres.

Chlorine - most often comes in tablet form and, although cheap, leaves an unpleasant taste and odour. The most effective and widely used version of Chlorine is Chlorine Dioxide, which is tasteless and odourless (produced by Potable Aqua and Lifesystems). It is also available from chemists in powder form as Chloramine-T and this is a cheap method of purifying large quantities of water. Chlorine is toxic in the event of overdose so care should be taken when diluting your solutions.

Method of Water Purification Using Chloramine-T
Dosage = 20mg per litre or 1g per 50 litres
  1. Measure 4g of Chloramine-T (take the top of a normal film canister [canisters vary so check before using], turn it upside down and level-fill the inside well, this is approximately 1g)
  2. Add to 100ml of water and shake well until completely dissolved
  3. Add 10ml (using a syringe) to each 20 litre jerry can
  4. Shake jerry can well and leave for 24 hrs before drinking

  5. Note: In case of river water etc. a double dose (1 gram per 25 litre water) should be applied and again the solution should be left for 24 hrs before drinking it

    Note: In case of immediate consumption 2 grams should be dissolved in 1 litre water plus 2 grams thiosulfate for neutralization of the Chloramine-T in order to protect the intestinal flora of the drinker (prevention of diarrhoea)

    Dosage information supplied by Axcentive, supplier of Halamid® (Chloramine-T)

    Alliance, who are agents of Axcentive, stipulate that you should contact your local authority with regard to local regulations when dosing with Halamid.

Silver nitrate - tasteless and odourless, silver nitrate comes in tablet form and is non-toxic in the event of overdose, but is a little expensive.

Potassium permanganate - This is another cheap and easy way to purify water. Potassium permanganate crystals can be bought from any chemist and you need add only about 3 or 4 crystals per litre of water (or until the water stains a light pink) and leave for 30 minutes. Potassium permanganate can also be used as a disinfectant for cleaning wounds, add crystals one by one until water turns purple (approx. 0.01% solution).

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Information published on this website is not a substitute for professional medical care or advice but should be used only as an aid in understanding current medical knowledge. A Doctor should always be consulted for any health problem or medical condition.

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