Safe drinking water


All outdoor groups require access to safe drinking water, whether carried, found in a drinkable condition, or treated by the party to ensure safety. Of all the illnesses and afflictions sufferred by bushwalking and skiing parties, water-borne contamination would be the most frequent after blisters. Many people would agree that few ailments make you feel worse than stomach and digestive tract illnesses. A knowledge of safe drinking water is very important.

Minimum water requirements

Experience suggests that the minimum daily water requirement in cool conditions is at least 2.5 - 3 litres per person per day, which rises to two or three times this amount in hot conditions, or when undertaking strenuous activity. Most bushwalkers seem to require around 3–4 litres per person for a ‘dry’ overnight camp.

When you consider that water weighs 1 kg per litre, plus the weight of the container, it is clear that any substantial quantity of water is prohibitively heavy to carry. Hence, there is a need on most trips to have access to safe drinking water along the way. Unfortunately, many available sources of water are unsuitable for immediate drinking without treatment. Reasons for this include progressive development of many bushwalking and skitouring areas, activities of other users of the bush, and thoughtless actions by many bushwalkers, skitourers and campers.


There is a wide variety of water contaminants which bushwalkers and ski tourers may encounter, summarised in Table 28.1. The dangers posed by, and best methods of treating them vary significantly. The following are some of the main contamination types.

Dissolved natural materials
Most bushwalkers have experienced salty or brackish water which is unpleasant to drink. Very salty water is clearly unsuitable to drink, and it is not possible to remove the salt with a portable device powered by bushwalkers. The only practical options are to follow the watercourse upstream until past the tidal zone, or look for a freshwater spring. The palatability of slightly brackish water can usually be improved with powdered drink flavourings such as Tang, lemon barley, etc. Slightly salty water does not pose much of a health threat on a short trip.

Water sources in cold rainforests (e.g. southwest Tasmania) often contain dissolved tannin, which gives the water a brown colour. This is generally regarded as harmless, although it may make drinks taste a bit strange, and tea seem stronger than it is! Some bushwalkers state that excess tannin can cause minor stomach upsets, although this does not seem to be formally reported in medical literature.

Suspended natural materials
Suspended natural materials include dirt, sticks and leaves, granite dust (mica) and various algal growths. Excluding algal growths, the overall threat posed by these contaminants is low, and they are more of a nuisance value.

Our rivers seem to be much more susceptible to major algal blooms in recent years, probably due to increased water diversion for agriculture and other uses, reduced baseline ecological flows and increased nutrient runoff from agricultural and unsewered areas. Much has been made of toxic blue-green algae, which does pose significant risks to outdoor groups.

It is worth knowing that not all toxic blue-green algae is physically coloured blue-green. Some are yellow or red-brown. Some blue-green algal blooms are toxic, others are not, and there is no way of telling without scientific laboratory analysis. The toxins are released when certain blue-green algal species die, and these dissolve into the water. Hence mechanical filtering, by itself, which removes the algae will not neutral-ise the toxins unless undertaken in conjunction with some form of activated-carbon filtration.

Algal contamination is relatively easy to detect, and is usually done from appearance (turgid, thick, gooey, coloured water) and smell (typical descriptions include earthy, pungent, musty, septic, nauseating, grassy, stench, ‘dead fish’ and ‘pigpen’). Determination of whether the contamination is toxic can only be done under laboratory conditions—hence, all coloured algal blooms must be treated as potentially toxic.

Toxic blue-green algae poses a severe threat due to the rapid and severe onset of symptoms, which can be fatal to livestock, although no human deaths have been reported in Australia of which we are aware. The toxins are in three categories:

  • nerve poisons, which block nerve messages to muscles, and can cause muscle tremors, staggering, paralysis, and respiratory failure
  • liver poisons, which can cause liver damage and promote tumour growth
  • skin irritants, which can cause gastroenteritis, skin and eye irritation, skin rashes and allergic reactions.

Further, algal blooms can affect huge quantities of water. Many will remember the toxic blue-green algal bloom in the Darling River, New South Wales in 1991–1992 which affected over 1000 km of river and caused a state of emergency to be declared.

These include solvents, heavy metals, fungicides, pesticides, weedicides and fertilisers. These have potential for significant health effects, some immediate and others being of more concern with long-term exposure. The sites of likely chemical contamination are readily identifiable – downstream of mines, industrial areas, sewage treatment plants and agricultural areas (the latter for pesticides, weedicides, excessive fertiliser runoff, etc.). Other than agricultural contamination, most of the other sources of chemical contamination are point sources and are usually readily avoided. Treatment of water from agricultural areas is difficult, but a combination of boiling and activated-carbon filtration will probably produce the best results.

Bacteria, virus, protozoa and other microscopic organisms
There is a huge variety of these organisms, the vast majority of which are not of significant threat to humans. The organisms of greatest threat are the parasites giardia and cryptosporidium, and the bacteria E. coli, which occurs in nearly all mammals’ faeces.

Giardia is now endemic in most high mountain streams in New South Wales (typically above 1100 m) and is also found in many other pristine-looking streams. Giardia is a parasite which can invade the human intestine, with a lifecycle of typically 10–14 days. Hence, symptoms will first occur 10–14 days after contamination, and outdoor activities of one and a half to two weeks before are often overlooked as a potential source of an illness. Infected people may endure several recurring bouts of the gia-rdia-induced illness before seeking medical diagnosis and treatment.

Giardia symptoms, which include diarrhoea and excessive wind, usually recur each 10–14 days, as the parasite passes through various stages of its lifecycle. Those who have had giardia usually report an offensive hydrogen sulphide (rotten-egg gas) odour in faeces and wind. The condition will not normally clear up without medical assistance, and a visit to the doctor is usually required, to prescribe a suitable intestinal antibiotic. As giardia lives in mountain streams as a relatively heavy cyst, collecting water from the surface of still pools is recommended as a simple precaution.

Cryptosporidium in small concentrations is relatively common in urban water supplies, and is spread by contamination of water sources with toilet waste, producing similar symptoms to giardia, but with a slight fever. E. coli contamination can produce diarrhoea, vomiting and other upset-stomach type infections, and can be of significant threat to the health and wellbeing of bushwalkers and ski tourers. E. coli contamination is common in unsewered areas, near high-use huts, below ski runs and in bushwalking areas where runoff from urban areas enters bushland, such as in the Blue Mountains, New South Wales.

Water purification methods

MechanicalActivated carbonIodine basedChlorine basedSilver basedUV light
filtrationfiltrationchemicalchemical treatmentchemical
(0.1–0.2 µm)treatmenttreatment
Virtually nilVirtually nilNilNilNilNil
Good but blocksGoodNilNilNilNil
filter rapidly
NilGoodIneffective: killsIneffective: killsNilProbably nil
algae but doesalgae but does
not neutralisenot neutralise
VariesVariesGenerally nilGenerally nilGenerally nilNil–low
VariesFair–goodGenerally nilGenerally nilGenerally nilNil
Generally lowFair–goodGenerally nilGenerally nilGenerally nilNil–low
Nil–lowNil–lowGoodGenerally goodVariesNil–good
  • Some benefit but low effectiveness against E. Coli.
  • Possibly best outcome if combined with iodine insert.
  • Filter life can vary significantly
  • Neutralises blue-green algae toxins
  • Also effective for chemical and heavy metal contamination, but these are probably avoidable.
  • Seems to be best solution
  • Takes 5-30 min to work.
  • Taste issue.
  • Not recommended for long-term use.
  • Good for E. Coli.
  • Ineffective against Giardia, the largest problem
  • Taste issue.
  • Not effective against Giardia or E. Coli, the major problems in Australia.
  • Effective only against Typhoid, Cholera etc, which are not major in Australia.
  • Useful for keeping water sweet under extended storage
  • Impractical for outdoor settings

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 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.

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.

The greatest threats

Most reports agree that the greatest wa-ter-borne dangers to bushwalkers and ski tourers are from giardia, E. coli and blue-green algae. For both giardia and E. coli, this is because of widespread potential contamination, difficulty of detecting contaminated water and the relative ease of becoming infected. In the case of giardia there is also the nearly universal need for medical treatment to counteract the infection. The main threats from blue-green algae are in the severe impact of toxins, the fact that uncontaminated water can be hard to find, and the potential for dehydration resulting from inability to find suitable water.

What to do with suspect water

Undoubtedly, the simplest, easiest and most practical treatment is boiling for approximately 10 minutes, as suggested by most authorities. Boiling does not assist with anything dissolved, including blue-green algae toxins, most chemicals and heavy metals.

Beyond boiling, most medical and scientific authorities which have investigated water-treatment approaches have concluded that the following treatments are most effective:

  • iodine-based chemical treatment for giardia, E. coli, bacteria, viruses and protozoa, in conjunction with;
  • activated-carbon filtration, which is generally effective against toxic blue-green algae, of benefit against chemical and heavy-metal contamination, and of some benefit against bacteria, viruses, etc.

Water treatment equipment

Mechanical filtration, iodine treatment and activated-carbon filtration require equipment for the purpose, but devices are available which combine methods. The selection of suitable, portable water treatment equipment will depend upon many things, but the following appear of highest relevance:

  • weight and filtering capacity
  • presence of both activated-carbon filtration and iodine-based treatment
  • filter life and availability of replacements
  • ease of use.

Most outdoor people would add price, which should consider both initial purchase, and the cost and frequency of ongoing filter replacement.

Further reading

Caffin R. 1994. Water fit to drink? Wild No. 54, 73–81.
Davis J. R. (Editor) 1997. Managing Algal Blooms. CSIRO, Canberra.
King, R 2000. Water filters and purifiers. Wild No. 77, 73–77.
Murray Darling Basin Commission. 1994. Blooming Blue Green Algae—Adult Study Circle Kit. MDBC, Canberra.