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Treat Questionable Water With Filters And Iodine, UA Microbiologist Says

June 12, 1997
University of Arizona
If you want to lie awake and worry before your next vacation, don't fret about bears in your camp or whether your plane will take a bath before reaching Europe. Worry about a greater threat -- pathogens in the water supply.
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Worry about something that's just as threatening, but much more common -- pathogens in the water supply. After all, on any given outing you're a lot more likely to run into microbes than bears or wind shear.

And these pathogens are something to worry about. They can be every bit as menacing as a 1,000-pound grizzly and a lot tougher than the wimps that spread common colds. Some of these bugs don't just ruin your trip. They can ruin your life.

Water-borne pathogens cause everything from severe, month-long bouts of diarrhea to heart disease, ulcers, and hepatitis.

Even places that look safe can be risky. University of Arizona microbiologist Charles P. Gerba and his students have spent a lot of time looking for (and finding) organisms in things like municipal water supplies, restaurant iced tea, non-carbonated bottled water from foreign countries, and the water in airplane rest rooms.

Gerba notes that some cities outside the U.S. treat their water but don't filter it, which is just the sort of thing some microbes can live with. Diarrhea-causing bugs like cryptosporidium and Giardia, for instance, are so resistant to chlorine that they sail right through water treatment plants. The only way to stop them is to physically filter the water.

Which is why backpackers and international travelers are lining up to buy point-of-use water filters. These hand-held units can be the best defense against questionable municipal water supplies and untreated backcountry streams.

But not all filters will do the job. Anyone can slap together a filter element and a couple of hoses, but that doesn't mean it will stop all the bacteria. "You need a good engineer to design these," Gerba says. If the seals don't hold up or water leaks past the filter element when pressure builds up, the microbes get a free ride into your glass.

So make sure the filter is registered with the EPA.

Gerba's lab does the majority of testing for EPA certification of point-of-use water filters and the procedure is rigorous. In fact, one technician in Gerba's lab does nothing but test filters.

"These are really mini water treatment plants and we have to make sure the units perform throughout their lifetimes," Gerba says. "The EPA tests give these filters some rough challenges."

Gerba recommends both filtering water and treating it with iodine. While some filters incorporate iodine treatment, most don't. Without iodine, filters stop bacteria that cause diarrhea, but they don't block viruses, which are much smaller.

Some backpackers skip the iodine tablets after filtering, figuring that few people in the backcountry means few disease-causing organisms. Gerba says they're taking a chance. "You never know what's happening upstream. People don't have to be using the areas near the water as a toilet, just bathing will do it."

Travelers also need to use their filters properly, Gerba says. The intake should always be isolated from the outlet. Even a single drop of untreated water can transfer disease organisms. (A lone virus just 4 millionths of an inch long is all that's needed to cause an infection.)

But what do you do when you can't use your filter? After all, even the most microbe paranoid among us shy away from pumping a water filter in full view of a crowded restaurant.

Drink bottled beer or canned soda, Gerba advises. But don't drink beer drawn from a tap or soda mixed from a machine. They can be contaminated. Outside of the U.S. and northern Europe, stay away from non-carbonated bottled water. Coliform bacteria have been found in bottled water from other countries. But carbonated bottled water is safe, Gerba adds. The pH is low enough that microbes can't survive.

Don't drink the tap water from airplane bathrooms because the tanks are sometimes refilled in countries where pathogens are common in the water supply. Travelers might even want to skip the meals loaded on at foreign airports. At least one planeload of passengers from South America contracted cholera.

Also stay away from raw vegetables. They often are contaminated in handling. Fruit is okay, if you peel and cut it yourself, Gerba says. In addition, avoid swimming and don't brush your teeth with untreated water.

No place is entirely safe. Anyone can be unlucky enough to run into that microbe with their name on it. But taking precautions -- especially when traveling outside the U.S. or into the backcountry -- can radically improve your chances of staying healthy.

Just pack your water filter and iodine tablets, follow a few simple precautions, and you can figure that you've done about all you can about the microbes.

Now it's time to lie awake worrying about lightning strikes on high peaks and the chances of having your passport stolen.


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The above story is based on materials provided by University of Arizona. Note: Materials may be edited for content and length.

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University of Arizona. "Treat Questionable Water With Filters And Iodine, UA Microbiologist Says." ScienceDaily. ScienceDaily, 12 June 1997. <>.
University of Arizona. (1997, June 12). Treat Questionable Water With Filters And Iodine, UA Microbiologist Says. ScienceDaily. Retrieved April 27, 2015 from
University of Arizona. "Treat Questionable Water With Filters And Iodine, UA Microbiologist Says." ScienceDaily. (accessed April 27, 2015).

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