Water Filters and Purifiers

Drinking pure water from clear-flowing stream surely is one of the fundamental joys of bushwalking. Unfortunately although it could be some of the cleanest, purest water on earth, any backcountry water source, no matter how high or remote, is susceptible

Drinking pure water from clear-flowing stream surely is one of the fundamental joys of bushwalking. Unfortunately although it could be some of the cleanest, purest water on earth, any backcountry water source, no matter how high or remote, is susceptible to contamination from microscopic pathogens (disease-causing agents) due to practices of the creatures that visit it, including birds, animals and humans. It is a fact of modern life, which experienced wilderness travellers recognise, you need to play it safe with water in the wilderness.


The three main types of water contaminants:

Suspended Matter
Floating debris such as leaves and sticks are not a problem. Silty or cloudy water containing a lot of clay, although unpleasant, is not a serious health risk unless it is combined with other pollutants. In most Australian bushland, a stream that is 'running dirty' without being in major flood usually indicates an unnatural, unstable catchment with eroding surfaces like farmland and dirt roads.

In alpine areas of other countries, some rivers are always discoloured by rock dust from glaciers upstream. Tea-coloured staining in otherwise clear water is common in Tasmania and many coastal areas. The cause is harmless tannic acid (as in tea!), naturally derived from the vegetation. Toxic blue-green algae may he present in streams with a very high input of nutrients which are flowing well below normal. Such water should not be drunk under any circumstances.

A filter is suitable for removing particulates. Preferably one that you can easily clean as silt and clay will quickly impede the flow rate.

Chemicals including pesticides, heavy metals and fertilisers may derive from farmlands, urban areas or point sources such as factories and dumps (which are often on the fringe of bushland). This sort of pollution is common in Australia generally, but not so prevalent in bushwalking areas. A Natural catchment is usually free of dangerous chemicals, except in some locations where the eroding refuse of old mine workings can contribute heavy metals.

Filters that include an activated carbon element offer some protection against such materials found in water. Iodine is the only chemical treatment that should be considered. If you believe a water source contains any chemicals or toxins, either boil the water (which offers limited benefit) or better, move on.

Bacteria, protozoa and viruses are perhaps the most insidious threat to good drinking water. Whenever animal or human fecal material connects with a water source, it is possible that pathogenic micro-organisms could invade the water. They fall into 3 categories:

Protozoan cysts — These are hard-shelled, single-cell parasites, the most well known being Giardia lamblia (ranging in size from 5 to 15 microns) and the resilient, lesser-known Cryptosporidium parvum (2 to 5 microns). Sources of these again include the faeces of both wild and domestic animals and those of humans. Unfortunately once Giardia is present in a catchment it might be there for good. It is a growing and potentially severe problem in Australia’s bushland.

Protozoan cysts range in size from 2 to 15 microns. They multiply in the digestive tract, where the cysts ""hatch."" Symptoms of Giardia (diarrhea, gas, nausea, cramps) appear within 1 to 2 weeks and last 4 to 6 weeks or longer. Symptoms of crypto (diarrhea, loose stool, cramps, upset stomach, slight fever) appear in 2 to 10 days and typically last 2 weeks. Giardiasis can be treated with prescription drugs; so far, cryptosporidiosis cannot. People with weakened immune systems could be at risk for more serious disease, particularly with cryptosporidiosis.

Portable filters and purifiers with fine pores, capable of trapping particles as small as 0.2 or 0.3 microns, reliably remove these bugs. Cryptosporidia are also highly resistant to iodine and chlorine.

Bacteria — These are smaller organisms, most of them commonly associated with food poisoning: E. coli, which is the main bacterium of concern, salmonella, cholera (common in some developing countries) and others. Sources of bacteria include domestic grazing animals, sewage plants, urban runoff and humans.

Bacteria range in size from 0.2 to 10 microns. Symptoms of infection (diarrhea is common) may appear within 6 hours or 3 to 5 days out. They may last 4 days or longer. In healthy people symptoms usually vanish within 5 days. Antibiotics can be used if needed.

Filters and purifiers are also effective in straining out these organisms.

Viruses — The tiniest of organisms, these include Hepatitis, rotavirus, Norwalk virus and polio. Viruses are the least common pathogens found in the wilderness (they are a significant threat in third world countries). Viruses that afflict humans usually only reach water sources via human fecal matter. Animals and humans, meanwhile, are common carriers of protozoa and bacteria.

Viruses range in size from 0.004 to 0.1 microns. Symptoms vary greatly for viral infection (acute gastroenteritis, diarrhea, nausea and jaundice), usually occurring within 1 to 2 weeks. Once exposed to the environment, viral particles exhibit a short lifespan and do not reproduce in water as some bacteria do.

Microfilters are incapable of trapping viruses but they can be inactivated by boiling, by contacting the chemical component found in purifiers, or by chemical treatment either before or after filtration.

A microscopic perspective
What is a micron? A micron is 1 millionth of a meter. A full stop at the end of a sentence is roughly 500 microns. The unaided human eye cannot see anything smaller than 50 microns. The straining ability of the pores in filters and purifiers is typically measured in microns, this is to allow a comparative measurement to the micro-organisms that you want to avoid. 
 You have 3 options for treating water:

1.  Boiling: Boiling is effective, very simple and is considered 100 percent effective against protozoan cysts, nontoxic bacteria and viruses. Bringing water to a rolling boil will kill the microorganisms in the water, if you are at altitude add 3 minutes longer, because of the lower boiling temperature. Boiling all water can take a lot of time and fuel, which will be very burdensome on a long trip.

Note: This is a method best suited to where the problem is limited, as when suspect water must be used for just one night rather than repeatedly. Boiling is an appropriate treatment for cooking water that is going to be boiled anyway.

2.  Chemical treatment: Exposing water to halogens such as iodine, silver or chlorine is believed to kill bacteria and viruses, but not all protozoan cysts. Being thick-walled organisms, Giardia and Cryptosporidia are resistant to chemical treatments, so microfiltration is recommended if you wish to be absolutely certain that the protozoan have been removed.

Halogens should also be given enough time to take effect, usually 10-15 minutes for pills to dissolve, very cold water or cloudy water requires a waiting period of 30-60 minutes (in either case read the directions carefully and follow them). If the treated water tastes to unpleasant then you can add either a neutralizing tablet, some powdered drink mix or run it through a carbon filter.

Note: Iodine is a very effective poison, including to humans in large quantities. Pregnant women should not use it or people who may be allergic to it and it can be unhealthy for people who use it for periods of longer than 14 days. Follow manufacturer instructions closely when using iodine or chlorine.

3.  Mechanical Filtration (microfilters and purifiers): The most popular solution to water contamination, these are specifically designed hand held devices that clean water via a mechanical process, forcing it through a finely porous internal element housed within a filtering unit.

Microfilters and purifiers both operate on the same mechanical principle. Using a hand pump and intake hose, both take in water from a creek or lake and force it through an internal element (a filtering ""medium""). This medium traps suspended elements, from fine sediment to invisible microorganisms, before giving out clean water.

Microfilters — are microbiological devices that remove bacteria (e.g. E.coli) and protozoan cysts (Giardia lamblia, Cryptosporidium) from contaminated water.

Purifiers — are microbiological devices that remove bacteria, protozoan cysts and viruses (e.g. hepatitis) from contaminated water.

Note: Viruses are too tiny to be trapped by a filter. Purifiers combine a filter with the addition of something that can render the viruses inactive, usually this is some form of iodine resin. Filter-makers contend that quality filters routinely capture 99 to 99.9 percent of viruses on the first pass since viruses (and bacteria) often become clumped with organic or mineral particles in water. These clumps are easy for filters to trap.

Does this mean purifiers are superior to microfilters?
Not necessarily, both offer a number of benefits that should be taken into account when you try to determine which system and what model will best answer your needs.

Here are some factors to consider before making your choice:
Simplicity of use – both systems use similar mechanical processes, differences in use are dependant more on individual models. Things to aware of are ease of maintenance, cleaning, storage of filters (do they need to be dried or treated before storage) and ease of moving water from the source through the treatment process and into your drinking container.

Capability of sustaining a steady, generous flow – this feature is determined by a combination of factors. The quality of the water source (heavy sediment load will impede flow), size of the pores in the filter (bigger pore size=faster flow potential), the surface area of the filter and the actual pumping action of the device.

Long-lasting – all microfilters and purifiers have a finite capacity. Purifiers are further restricted by the effectiveness of the additional purifying component, which have a much shorter life than the filter component itself.

Note: To tell if a filter or purifier delivers in these areas, look for clues in the specification chart that come with them. Remember the composition of the filter medium contributes greatly to the quality and cost of the unit.

Questions to ask yourself

  • How often are you likely to treat water?
  • How much water do you need to treat at any one time?
  • Which pollutants do you want to remove?
  • How much do you want to spend?
  • Is iodine consumption is an issue?

Some handy tips

  • Avoid filtering water in area where animal or human activity is obvious.
  • Try and filter water from still, clear water sources. Many microorganisms tend to sink to the bottom of still water; a turbulent stream keeps them suspended.
  • Rather than filter directly from the creek or lake, put water in a pot and filter from that. This gives you a chance to examine exactly how the water looks before you send it through your filter. This helps prevent clogging. If the water is cloudy, let it sit in the pot for an hour or so, then skim the clearest water off the top.
  • When you clean your filter, recognize you are handling a potentially contaminated object. Don't handle food or put your hands to your mouth after cleaning your filter.
  • Follow manufacturer instructions for cleaning and storage. At home, consider pumping a weak bleach-and-water solution through the filter to sterilize it. If you can disassemble your unit, allow it to dry out completely before storing it.
  • Humans can survive for an amazingly long time without food, but must have water regularly. Dehydration can cause heat stroke, hypothermia, frostbite, mountain sickness and death. Drink regularly; even when you don't feel thirsty.
  • In the summer you need at least three or four litres each day. In cold conditions your metabolism speeds up to generate more heat, so add an extra litre per day in the winter or above the snow line. Keep track of urine output: you should urinate at least three times a day. The liquid should be clear or light-coloured; a dark yellow colour is a sign of dehydration


Sourced from Paddy Pallin