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Introduction

Why worry about drinking water?

Many people jump on a plane or head into the wilds without a thought about the purity of their drinking water. They live by the mantra of ignorance: ‘What I can’t see won’t hurt me’ or great bravado: ‘I have cast iron stomach’ as they drink from the nearest creek or lake. The bad news is that what you can’t see will hurt you, and might even kill you, and nobody’s stomach can repel the pathogens found in our streams, rivers and lakes.

The worldwide rate of infection by waterborne pathogens—bacteria, viruses, protozoa, and parasitic worms that make people sick—is as astounding. For example, an estimated one and a half billion people, mostly in Asia and Africa, are infected with Ascaris lumbricoides, a 30 centimetre long parasitic intestinal roundworm that produces 200,000 eggs per day. Many water supplies in developing nations are also cesspools of chemicals, dioxins, heavy metals, and pesticides, often banned in North America, but still used extensively in other parts of the world.

In North America and Europe we are fortunate that only a fraction of the world’s pathogens and chemicals contaminate our backcountry and recreational water supplies, but in many cases our mountain streams are anything but pristine. Literature on waterborne pathogens in developed countries mainly focuses on Giardia as the waterborne enemy of humans. This attention is largely justified because the organism infects most North American and European waterways. However, in the 1990s, outbreaks of Cryptosporidium in Milwaukee, Wisconsin, USA and Kelowna, B.C. Canada raised awareness of the gut wrenching potential of this protozoan, which is highly resistant to chlorine disinfection.

Often, however, other protozoa, bacteria, viruses, worm parasites, and chemical pollutants are ignored, giving the impression that Giardia and Cryptosporidium are the only forces to be reckoned with in backcountry and recreational water. People have been led to believe that other sources of infection, especially viruses, are only a ‘Third World’ problem. Nothing could be further from the truth. While many organisms are far more prevalent in the tropics than developed countries, many live happily in people’s bowels north of the Mexican border and the Mediterranean Sea. We even have our own cosmopolitan organisms, such as pinworms, that are more prevalent here than anywhere else in the world.

Besides waterborne pathogens, our massive use of chemical fertilizers and gratuitous heavy industry have made many rivers and lakes into chemical sewers. Cities, industrial sites, wellheads, mines and pulp mills routinely leech cyanide, mercury, and carcinogenic dioxins into waterways. Many of the huge subterranean aquifers of North America and Europe are polluted with fertilizers and pesticides. As well, acid rain and airborne particles have ensured that even remote glacier fed mountain lakes can display disturbing levels of industrial chemicals.

The Pathogen Risks in Drinking Water

Microbiologists have calculated that of the 100 trillion (1014) cells in the average adult human body only ten trillion (1013) are human cells while the other 90%, or 90 trillion (9×1013) cells, are bacteria, fungi, protozoa and non-microscopic parasites. Some, thankfully few, of these ‘guest’ organisms are pathogenic, meaning they cause people to get sick.

Waterborne pathogens are classified as bacteria, viruses, protozoan parasites or helminthes (worm parasites). Except for their ability to infect humans, these organisms are not related to one another. Each group has a distinct physiology and process by which it infects humans. Fortunately, the human body has a highly-evolved defense system against pathogenic invaders that enter through the mouth. The greatest barrier is the highly acidic stomach, however, in large enough numbers or when carried quickly through the stomach in water, pathogens can reach the intestine and cause infection.

So why all the disease then?

The Faecal–Oral Problem

The simple reason is that infected people excrete massive numbers of pathogens in their feaces, many of which get into the water supply. With all of the nasty things in the water supply, it is almost inevitable that we will eat some in food or untreated drinking water and continue the cycle. For obvious reasons, this is known as the faecal–oral route of transmission.

People infected with a pathogen, even those who do not seem to be sick, known as asymptomatic carriers, excrete pathogens in their faeces. The volume of pathogens shed in human faeces is enormous and can exceed 100 million (109) organisms per gram of faeces.

In the annual reported cases of Salmonella infection in the US, Americans alone shed, thankfully mostly into the toilet, a staggering 6.314–6.316 Salmonella bacteria. Even more prolific are Giardia, which infect humans, deer, elk, cattle, rodents, and of course the humble beaver from which the illness Giardiasis takes the popular name ‘Beaver Fever.’

The end result is that humans and animals are veritable mobile manufacturing plants for pathogens. A single person can hike around a wilderness area and deposit trillions of pathogens into the environment in a few days.

Besides naturally occurring pathogens, international travel has amplified and accelerated the spread of some pathogens not normally found in waters of the northern hemisphere. This is especially important in tourist zones such as Banff National Park, Alberta, Whistler, British Columbia, Yosemite, California and the the heavily travelled mountain regions of Europe.

Millions of tourists defecate daily in these areas. Their millions of kilograms of faeces enter waterways after treatment that ranges from first rate in some towns to none in many hiking and trekking areas. Some of these travellers are infected with pathogens, many of which are not native to their part of the world. In spite of the environmental factors working against the survival of pathogens such as UV radiation, temperature extremes, water pH and predatory microorganisms, there are plenty out there waiting to visit a welcoming intestine and carry on the cycle.