The aim of water treatment is to remove contaminants or reduce them to a concentration that means the water is safe to drink. Safe drinking water does not have to be sterile, and can contain organic and inorganic matter that the body can tolerate. Contaminants include sediments and pathogens (bacteria, viruses, protozoa, larger organisms (worms) or salts and toxins (fertilisers, heavy metals). Most commonly, water supplies are contaminated by human or animal excrement, or occasionally a dead animal carcass ends up in the water supply (e.g. cattle crossing a river). Contamination can also occur in the form of pollutants from human infrastructure such as mining or farming.

Common pathogenic parasitic infections in humans include Giardia, Cryptosporidium (protozoans) and E. coli (a common bacteria), all of which are transmitted via contaminated water of poor hygiene. Symptoms vary from stomach cramps and fatigue though to bloating and diarrhoea.

A pathology test can quickly distinguish Giardia from Cryptosporidium, but on a bushwalk the symptoms of stomach and intestinal upset are very similar. Instead, these types of infections are generally referred to as Traveller’s diarrhoea. Good hygiene practice and care of food and water are the best ways to prevent getting sick in the bush. Prevention is better than cure!

There is no practical way to be sure if the water is safe to drink, so if in doubt treat it. In general, on day walks that start from home and built up areas take all water you need from a tap. Day walks are often close to farms, houses, mines or other places that mean the water is likely contaminated. Also, on most day walks it is easy enough to carry enough water for the day. The exception of longer day walks especially when it’s hot. You may need to plan for water collection and treatment.

On overnight and longer walks, it’s probable that water will be of a higher quality, but again there is no way to be sure. As the number of people walking or travelling through the remote areas increases, so does the chance of water being polluted by human waste. For example, parts of Tasmania’s Overland Track have water pollution, from human wastes. Some people choose to drink straight from creeks where there are no more campsites, tracks, huts or other potential pollutant sources, upstream. The risk of getting sick whilst in remote areas comes with significant consequences, generally best to err on the side of caution and treat the water.

Individual health and immune strength is also a factor: everyone’s immune system is different, and tolerance levels to pathogen contaminants vary. Diseases that affect the immune system like HIV and diabetes mean that some people may be much more susceptible to pathogens. Pregnant women are also at higher risk. Therefore, individuals who are immunocompromised (i.e. an impaired immune system) would be wise to take extra precaution and treat all water and to speak with their doctor about the best methods for them. Likewise, overseas travellers often don’t risk drinking the same water supplies as locals because their immune systems have not had time to build adequate resistance. This is often why travellers are advised to drink bottled water only.

Infection of waterborne pathogens can also occur from using contaminated water to wash or cook or from physical contact with an infected person, “hand to mouth” transmission. According to a study of the risk of giardiasis from consumption of wilderness water in North America, the incidence of giardia in wilderness walkers is high, however, the infections are more likely caused by poor hygiene rather than contaminated water[note]Welch TP (2000). Risk of giardiasis from consumption of wilderness water in North America: a systematic review of epidemiologic data. International Journal of Infectious Diseases 4 (2): 100–103[/note]. Regular use of antibacterial gels after toileting and before food preparation and consumption on a bushwalk can reduce the likelihood and spread of infection.

But while the body can fight some pathogens to some degree, it’s a different story for some materials that can accumulate in the body. Long-term use of water contaminated with heavy metals can have severe health implications because the metals can bind to cellular matter and interfere with essential processes[note]Landis, WG; Sofield, RM; Yu, M-H (2000). Introduction to Environmental Toxicology: Molecular Substructures to Ecological Landscapes. 4th: CRC Press[/note]. Heavy metals have carcinogenic properties and can interfere with respiratory and circulatory systems. Unlike water sources that are pathogen-infected, water sources that contain heavy metals cannot easily be treated to make them safe in the field and should, therefore, be avoided unless in an emergency.

In short, choosing to treat water comes down to good judgement, if in doubt treat it and encourage people in your group to use good personal hygiene practices.

Water can be contaminated by living things such as bacteria, viruses and protozoa, and non-living things such as sediment, dissolved tannins, fertilizers and heavy metals. The differing sizes and nature of these contaminants mean that some water purification methods work on some contaminants but not others.

Without optical aids, it’s only possible to identify large sediment. Anything smaller than what the naked eye can see requires more complex microbiological tests to determine their presence. In some cases, water is coloured by soluble vegetation or peat matter, known as tannins. Tannin coloured water is perfectly fine to drink without treatment, despite what some people perceive as an unpalatable colour.

Large sediments are any visible biological material in or floating in the water source. These include leaves, sticks, mud; and other organic debris such as plant and animal matter.

Removing sediments or other large organic matter may make subsequent water treatment more effective. This is particularly true for chemical treatments where the active chemical particles tend to bind to organic matter, thus reducing their effectiveness.

An effective way of removing sediments is to filter the water through cloth. Collect water in a large billy and filter it into smaller containers. Clothing fabric filters well because they are strong enough to catch organic material but still allows the much smaller water particles through the holes in the fabric. A hat or bandana works well.

Filtered water still contains pathogens, so a decision needs to be made if further treatment is required.

Pathogens can make humans sick by challenging the immune system. Some pathogens kill cells or disrupt cell function, and others produce toxic waste products. Sometimes pathogens multiply so quickly that they crowd out the host tissues, disrupting normal function. The immune system fights back with chemical secretion, antibodies and fever, a heat response aimed at killing pathogens.

Consuming too many pathogens can cause mild to severe illness in humans and can lead to death, particularly in parts of the world where people do not have access to clean drinking water[note]Montgomery, M. A. & Elimelech, M. Water and sanitation in developing countries: including health in the equation. Environment Science Technology 41, 17–24 (2007)[/note].

Pathogens most harmful to humans include microscopic viruses, bacteria and protozoa as well as larger organisms such as worms.

Viruses are much smaller than bacteria or protozoa, and need to occupy another living cell to replicate. They are infectious agents that can attack a variety of living things from bacteria and protozoa through to animals and plants.

Bacteria are single-celled prokaryote organisms that are a few micrometres in length. Bacteria were one of the first forms of life to appear on earth, and are renowned for being able to survive in soil and water as well as extreme conditions such as radioactive waste and acidic springs.

Protozoa are single-celled eukaryote organisms that are generally bigger than bacterial cells and contain different cell contents.

Parasitic worms are more evolutionarily complex than viruses, protozoa and bacteria being multi-celled eukaryote organisms. Although they can survive independently, many species use another host organism to reproduce and spread. They can enter the human body in cyst or adult form via food and drink or bites from insects like mosquitoes and often reside on the skin or in the intestines. Humans suffer discomfort and illness from such infections including diarrhoea, fatigue and skin rashes.

Pathogens can generally be removed by:

• Micro-filtering (e.g. microfilter by pumping, or LifeStraw
• Chemical inactivation (e.g. iodine, micropure)
• Boiling and
• UV treatment.

Toxins can make people really unwell by poisoning the body. Sometimes, toxins only need to be in small concentrations to cause problems. In other cases, it’s the accumulation of toxins over an extended period of time that causes health problems. This is particularly a concern for people ingesting water from industrial run-off in areas that do not have adequate regulation of clean drinking water.

Toxins of concern include fertilisers, made of nitrogen, phosphorous and potassium. These can cause serious environmental damage and health risks to humans when found in waterways. Once fertilisers reach waterways, they enrich nutrients so much that some plant populations explode in quantity. Large amounts of blue-green algae is a sign of this Eutrophication process, and this algae produces toxins which go on to poison animals and humans alike.

Heavy metal runoff is another toxin of concern. For example, mercury runoff into water systems occurs via industry processes including coal and gold mining, Chlor-alkali plants and Trash incinerators. Mercury poisoning in humans can lead to itchy skin, swelling and skin discolouration, and at extreme levels of exposure, muscular weakness and mental confusion. Mercury poisoning is usually caused by consumption of aquatic produce where mercury has bioaccumulated. Mad Hatter disease was a chronic syndrome among hat makers who had prolonged exposure to mercury vapours. The “Mad Hatter” from Lewis Carroll‘s Alice’s Adventures in Wonderland is renowned for his eccentric behaviour.

Toxins cannot be removed by chemical or UV treatment, and boiling will only concentrate the toxins further. Instead, chemicals must be filtered out, a process that requires special equipment as it requires filtration at the atomic scale. While some hiking filters may claim to reduce toxins such as mercury, they are unlikely to remove such contaminations completely.

From a practical sense, if pushed for water supplies, drinking low levels of water containing toxins is probably not going to have ongoing effects, but continual use is unwise. It’s dangerous to consume fish or other aquatic food from these systems because toxins tend to bioaccumulate in aquatic organisms to levels that are very dangerous.

Saltwater typically refers to ocean water with high concentrations of sodium chloride. Saltwater is unpalatable and drinking it will lead to dehydration. But drinking water also contains other types of salts at palatable levels.

Tap water contains some salts, which varies with the source. This is why tap water tastes funny when drinking from a source that’s different to usual. In appropriate quantities, the following salts are not a problem:

• Calcium and magnesium – these describe the hardness of water
• Sulphates such as magnesium sulfate, calcium sulfate or sodium sulphate
• Iron from rock deposits and
• Chlorides, either naturally occurring or from industry.

As with toxins, salts are challenging to remove in the field as the process requires atom-sized filtering systems. Small hand-held units use portable reverse osmosis to purify water. The Katadyn Survivor 06, which produces 0.89 litres of water per hour at a pumping frequency of 40 pumps per minute. Given the effort required, it’s better to select a freshwater source where possible and only use desal unit in an emergency situation.

There are a number of ways to make water palatable in the field, each with different merits on ease and effectiveness of decontaminating water. Often, it’s worth having a few options available in case one fails.

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Editor’s pick: Lightweight UV radiation pen with a backup of chemical tablets.

The boiling method is used for killing living contaminants (bacteria, viruses and protozoa) found in a water supply. It does not sterilise the water, but instead, damages living pathogens enough to kill or prevent them from replicating.

Water must be heated to boiling point 100℃ at sea level then have a rolling boil for at least one minute, and three minutes if above 2000 metre altitude. Since water boils at a lower temperature at higher altitudes, the extra time accounts for the difference in temperature.

Advantage: no specialised equipment required since billy and stove is already part of usual multi-day bushwalking gear.
Disadvantages: Water takes time and fuel to treat, and time to cool down enough to drink or decant to other containers. Hard to do efficiently in large quantities quickly. Extra fuel is needed.

Chemical treatments are effective against viruses, bacteria, protozoa. Examples of chemical treatments include

Iodine denatures proteins in any living matter. 2% formulation five drops per litre, ten drops per litre if cloudy. Allow to stand for 30 minutes before drinking.

Advantages: Likely to be already carrying this in your first aid kit. Lightweight.
Disadvantages: takes time to be effective. Unpleasant chemical taste, potential adverse health effects if used for prolonged periods.

Chlorine Dioxide products sterilizes water by disrupting critical processes by living matter. Micropure tablets – use one tablet for 1 litre of water and take 30 minutes for bacteria and viruses, 2 hours for Giardia in clear water. Aquamira drops require two solutions to be mixed and take 15 minutes to treat water.

Advantages: Generally accepted to be more effective than iodine, better tasting and better for health. Lightweight.
Disadvantages: Must be careful to pack the tablets so that they don’t get crushed. Takes time for water to be safe to drink (30 minutes – 2 hours). May have to pre-filter water if organic substances are present because they will inactivate many chemical treatments.

Radiation treatment is effective against viruses, bacteria and protozoa. UV light sterilizes water by damaging the nucleic acids of pathogens that are involved in reproduction. Cellular RNA and DNA absorb UV energy, which breaks necessary bonds in these molecules. Without the ability to reproduce the pathogens cannot spread and infect. So UV light do not kill or remove pathogens, but rather de-activates them.

The steripen can sterilise 0.5 L water in a minute. It is generally most effective against bacteria and viruses, and less so against Protozoa because of their thicker cell wall. The water source is preferably as clear as possible because any organic matter in the water reduces the effectiveness of the UV treatment by absorbing UV light. Users must remember to recharge for every trip, and carry spare batteries for extended trips.

Advantages: Water immediately ready to drink; doesn’t taste funny.
Disadvantage: Need to carry backup water purification methods in case of machine failure or batteries running out in the field.

Filtration can be used to remove macroparticles using cloth fabric or microparticles using specialised pumps.

1 Macro-filter using fabric
Most simply, fabric-filtering removes large sediments include floating leaves, sticks, mud and other debris, but no harmful pathogens. Water can be effectively filtered through a clean t-shirt, handkerchief, bandana, coffee filter paper or a commercial pre-filter.

Advantage: no specialised equipment required other than clothes!
Disadvantage: doesn’t remove harmful pathogens

2 Microfilter using a pump
Microfilter pumps remove bacteria, protozoa, cysts and sediments, and sometimes but not always viruses. In general, water is pumped through pores of 0.2-0.3 µm diameter depending on the model, leaving bacteria, protozoa, cysts and sediments behind. The Katadyn Hiker Pro does 1 L/min. Filters and cartridges may need regular replacement depending on how dirty the water is.

Advantage: Water is ready very quickly (the “Katadyn Hiker Pro” does 1 L/minute).
Disadvantages: Need to carry backup water purification methods in case pump breaks in the field; does not necessarily remove viruses. Technical support from Katadyn says:
“Due to their tiny size, viruses can theoretically not be removed with a 0.2 micron (or any physical) filter. Nevertheless, long-term experience in the field has indicated that Katadyn Filters can retain viruses. This surprising fact can be explained: Viruses have an electrical surface charge that attaches them to other particles or materials. Therefore, the tight pore structure of the Katadyn Filters removes the viruses attached to particles from your drinking water.”

3. Microfilter by sucking
A much cheaper form of filtration is the LifeStraw, where the user sucks clean water through a filter before drinking. This method removes bacteria, protozoa, cysts and sediments, but not microscopic minerals, chemicals and viruses. Water is pumped through pores (0.2-0.3 µm diameter depending on model) leaving bacteria, protozoa, cysts and sediments behind. This lasts for 1000 litres (approximately a year of drinking water).

Advantages: Water immediately drinkable. Filter lasts for approximately a year.
Disadvantages: Doesn’t remove microscopic minerals, chemicals, or viruses. Only can be used by one person at a time. Short straw length means that you need to be at the water source to drink. That is, clean water cannot be carried to camp. Alternatively, stick it into a wide-brimmed water bottle, but this can be fiddly. An alternative is the Sawyer bottle.

While humans cannot drink salt water straight, it’s possible to use a de-sal unit to make the water palatable.

Portable reverse osmosis units are available and can be used in emergency situations. They work by manually pumping water through a semipermeable membrane that removes enough salt to make it palatable. The size of the pores are so small that extremely pure drinking water is produced, but the process is slow. Katadyn claims to have the world’s smallest desal unit called the Survivor 06, which produces 0.89 litres of water per hour at a pumping frequency of 40 pumps per minute. While this is achievable in an emergency situation, it’s not that practical on a multi-day coastal bushwalk.

Managing an upset stomach in the bush
An upset stomach is unpleasant at the best of times, particularly on a bushwalk. They’re relatively uncommon, however, being prepared with a handy trowel, plenty of toilet paper, antibacterial gel and baby wipes can make stomach upsets easier to manage in the field.

If possible, after a stomach upset, lie low for a day or two at a base camp. Adding gastrolyte tablets to water can be a good way of rehydrating, as bouts of diarrhoea or vomiting mean significant water losses.

Once back home, if symptoms persist, seek medical attention, where stool samples can be used to test for infection and treatment can be given.

Managing water containers
Having a well-organised water container system avoids mix-ups between treated and untreated water, particularly when the treatment process can take time to be effective, such as chemical.

There are a few options:

• Colour coded or labelled bottles to easily identify treated from untreated water. This works well for treatments that take time.
• A large source bladder with untreated water that is decanted into drinking bottles as it is treated. This works well for UV treatments or filtration treatments.

Stomaching distasteful water
Nasty tasting water can be unpleasant to drink but unavoidable in some scenarios. Sometimes water sources are heavy with tannins or have relatively high salt content, such as bore water. In these cases, the water is less palatable than water people are generally used to, and some people can find it hard to drink.

A few ways to solve this.
On the track:

• Add light cordial powders or sugar
• Set drinking goals by measuring the amount of water consumed. This can reduce the risk of dehydration
• Filtering using a pump can remove sediment, tannins, heavy metals and bad taste.

At camp:

• Make tea
• Drink leftover water from boiled vegetables – packed with flavour apparently. Perhaps likewise for pasta and rice?

Backup treatment options
People generally develop a favourite way of treating water, and that’s what they carry. But it’s sensible to carry some backup in case things go wrong. Anything relying on a battery can run out. Tablets can get lost or waterlogged. Make sure there are some backups in the group, especially when walking in areas with lots of campers or downstream from houses, farms or industrial dwellings.