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The Soft Machine: Travel Health column

Boil, filter or bleach it...however you treat it, if you can't turn it into wine, at least make sure the water you're drinking is safe


Carrie Beallor, BScOT, MD, CCFP, is a graduate of the University of Toronto medical school and is currently practicing family medicine with a special interest in pre- and post-travel medicine.
(Photo by Robert J. Brodey)

AS LONG AS YOU'RE eating feces, you'll likely get traveller's diarrhea. Though people rarely intend to eat feces, it is micro-organisms from human and animal waste which are the most common source of contaminated drinking water causing disease. Contrary to popular belief, impurities in water cannot be sensed by sight, smell or taste. A cup of crisp, cool, clear water can be quite deceiving -- both in the developing and the developed worlds.

Consider the things you might not be able to see, smell or taste: bacteria like E. Coli, campylobacter or cholera, viruses like hepatitis A or rotavirus, protozoa like giardia or cryptosporidium and parasites like tapeworms or flukes. Other non-living substances might include heavy metals, nitrates, pesticides, herbicides and a plethora of other chemicals used in industry, agriculture and recreation.

With that as an introduction, you might wonder why drink the water at all once you've left home. But the human body is made up of more than 60 per cent water and we need a minimum average of two litres of water per day. When travelling to areas with questionable water quality, it is best to avoid disease by treating the water. There are a variety of ways to do this.

Heat: Different bugs are killed at different temperatures, but the general rule of thumb is to boil water for one minute to kill harmful pathogens. Most bacteria, viruses and protozoa will be killed in one minute at 70*C. Boiling at 100*C is effective at sea level and even above 3,000 metres, where the boiling point is 90*C. Some sources, however, recommend allowing three minutes of boiling time at high altitude for added safety.

Filtration: Filters are used to physically remove micro-organisms and other tiny particles of matter. They either have a single layer of pores, ideally smaller than the smallest organism, or are depth filters which trap particles. You need pore sizes of 0.2um to remove bacteria, 5um for giardia, 2um for cryptosporidia, and 20um to remove parasitic eggs and larvae. Most filters are not adequate to remove viruses, which are very small. Filters are portable, easy to use and don't add a bad taste to the water, but disadvantages include the fact that they clog quickly with turbid water and require cartridge changes over time; they can be bulky, and if damaged, can be rendered ineffective. Filters are ideal when bacteria and cysts are the concern but viral contamination is not an issue.

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