Ways to treat water

There are a large number of ways of treating water, which have varying degrees of effectiveness against various forms of contamination, described below and also summarised in Table 28.1.

The following all have effectiveness in some circumstances in making water suitable to drink.

Boiling
Boiling water can be effective against many bacteria, viruses, protozoa, etc. It is generally recommended that water must be boiled for up to ten minutes to be generally effective. At higher altitudes, water boils at a lower temperature, hence boiling for a longer period is required above approximately 1500–2000 m.

Charcoal
An old bushy’s trick to clear muddy water is to place a piece of charcoal in the bottom of the container, and let the water stand. For clearing suspended earth and mud, this can be surprisingly effective. However, it has little effect against other contaminants.

Cloth filtration
A clean handkerchief or similar cloth can be useful for removing suspended natural material such as dirt, sticks, and leaves but has little effect against most other contaminants.

Mechanical filtration
Many commercially available portable water treatment devices use mechanical filtration (0.2–0.2 microns), usually in combination with other treatments described below. Mechanical filtration by itself is of benefit against giardia and cryptosporidium, of some benefit against bacteria, but cannot remove viruses, as viruses are much smaller than the pores in currently available filters.

Activated-carbon filtration
This is the best method to treat blue-green algae toxins (although filters tend to block rapidly, where pre-filtration with a coffee filter can help). It is also effective against contamination from many chemicals and heavy metals. There is less evidence that activated-carbon filtration is effective against bacteria, viruses, or protozoa.

Iodine-based chemical treatment
This is generally regarded as the most effective general treatment against bacteria, viruses, and protozoa, including giardia and E. coli. Iodine chemical treatment is ineffective against blue-green algae—while it kills the algae, it does not neutralise the toxins, which pose the main threat. Long-term iodine use (over periods of weeks or months) has been linked to liver damage, but this is unlikely to be a problem on relatively short trips. Pregnant women, or people with thyroid conditions should not take iodine.

Iodine water purification tablets are generally recommended over liquid iodine, as the dose is more consistent, and the taste usually less obtrusive, but treated water does have a salty, chemical taste. It is important to note that water must be left to stand for at least 30 minutes for treatment effectiveness, and longer at low temperatures and if the water is murky. If the time the water is left standing before consumption is increased, the concentration of iodine can be reduced without reducing effectiveness, which improves the taste. Vitamin C (ascorbic acid) neutralises the iodine – iodide reaction, and also improves the salty taste. Vitamin C must be added after the water is treated and left to stand.

Chlorine-based chemical treatment
This is generally effective against E. coli and viruses but is of doubtful effectiveness against giardia and cryptosporidium, and is generally ineffective against most other contaminants. Chlorine-treated water also tends to be unpalatable and usually tastes like drinking a swimming pool!

Silver-based chemical treatment
This is effective against typhoid, cholera and similar diseases which are not major problems in Australia, but is not generally effective against giardia or E. coli. However, it is recommended to keep water sweet for extended periods of storage away from air, such as for water barrels left in the field for use on a later trip.

Ultraviolet light
Many commercial water treatment plants use ultraviolet (UV) light treatment, which is generally effective at killing many bacteria, viruses, and similar mi-cro-organisms. However, it is impractical for outdoor circumstances.