All the guide books tell you to boil, filter and chemically treat all water and I will too just to cover my butt in the event of liability issues. I always disregard this good advice, drinking directly from the stream, and thus far have never been sick. If you choose to enjoy the taste of unadulterated stream water too then you did so of your own volition. If the water made you sick then it’s your fault and not the fault of this book or the bear which crapped upstream.
Whatever your choice is get your water from clear running brooks not from lakes or ponds. Water from snow pack is better than water from glaciers. The latter contains too much clay. Carry lots of water, at least 40 litres, whenever kayaking as good water can be surprisingly hard to find on the wet coast of Canada. A green algae bloom in tide pools or wet patches trickling across a beach does not mean something horrible died in the water. It just means the water is brackish. Freshwater will be found up the slope.
Giardia cysts can exist under the most pristine, wilderness conditions. Clear running water is not a sure sign that it is drinkable.
Illustration by Manami Kimura
If your source of water is at a popular camping spot then go upstream away from the camp to get your drinking water. Take great pains to clean yourself and your dishes or clothing well away from the bank of any water body or the water will become polluted. Leftover food does not belong in the water. If fires are allowed and it is safe to do so, burn it. Try to avoid using soaps or detergents but when you must only use the biodegradable kind available from outdoor stores.
Beavers have gotten a bad rap, taking most of the blame for spreading a disease that can just as easily be passed into the water system by deer, muskrats, raccoons, coyotes and squirrels. Indeed any mammal including domestic pets, livestock and humans are guilty of carrying the protozoan parasite into the backcountry.
Giardia lambia, as the microbe is called, enters the environment in hardy cyst form where it can survive for weeks at a time. Giardia cysts can exist under the most pristine, wilderness conditions. Clear running water is not a sure sign that it is drinkable. Ingestation of a single cyst is enough to cause infection in humans. The hard, capsule-like shell dissolves, releasing the infectious form of the parasite which multiplies exponentially.
Full-blown giardiasis may take from 5 to 25 days to manifest itself though symptoms typically appear within 10 days. The giardia protozoa latch themselves on to the intestinal tract, severely impairing the body's ability to absorb nutrients and water. Food and water pass straight through the digestive system instead, appearing as the principal symptom of giardiasis, diarrhea. Infection usually lasts for around two weeks and is usually treated with antibiotics though some individuals may never show symptoms at all and others recover without treatment. Giardiasis has been known to persist for months on end in those with weakened immune systems.
The best treatment of course is prevention and prevention typically means water purification. The surest method of water treatment is boiling. Five minutes at a steady boil will destroy every living organism in the water. Additional time is needed at higher elevations. Boiled water can be bland and dull tasting. Shaking oxygen back into it will help improve the taste.
Expensive, heavy filters are available which claim to strain out giardia lambia. Studies have shown however that not all filters are effective. In order to effectively purify water the filter porousness must be no bigger than 0.2 microns. Such fine filters are hard to pump but produce great tasting water. Chlorine-based water treatments are not effective against giardia cysts. Iodine treatments fare better but studies have shown that a typical 20 minute treatment is not enough to eliminate all cysts. Eight hours is the minimum required for effective iodine treatment. Iodized water tastes horrible however and in rare cases may cause thyroid problems.