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.