Water Treatment for International Travel

 Woman fills water bottle from stream

Water quality can vary widely outside the United States, and it is particularly suspect in developing countries. So what is the best method of water treatment for international travel?

In most cases, the recommended strategy involves using a method (mechanical, electronic or chemical) designated as a water purifier, which eliminates viruses as well as protozoa and bacteria.

Purifiers Versus Filters

Water-related illness is typically linked to 1 of 3 types of invisible-to-the-eye pathogens (disease-carrying pests). Caused by animal or human contamination, principally via fecal matter, the following trio of bad boys is potentially lurking in just about any lake, river or stream outside the U.S. and Canada:

  • Protozoa and cysts (Cryptosporidium parvum, Giardia lamblia). Single-cell parasites; tiny (between 1 and 20 microns. A micron is 1-millionth of a meter, or 0.00004 inch. The period at the end of this sentence is roughly 500 microns.)
  • Bacteria (Escherichia coli, or E. coli, Salmonella, Vibrio cholerae, Yersinia entercolitica, Leptospira interrogans and many others). Very tiny (0.1 to 10 microns).
  • Viruses (hepatitis A, rotavirus, enterovirus, norovirus). Exceptionally tiny (0.005 to 0.1 micron). Caused by human waste.

Of the portable water-treatment methods offered at REI, any designated as a "purifier" will rid water of all 3 threats. Pump or gravity-based devices commonly called "filters" reliably sift out protozoa, cysts and bacteria but are not effective against miniscule viruses. Water can also be purified (the technical term is "disinfected") by some chemicals and chemical-based devices.

Handheld water filters designed for backcountry travel are more correctly called "microfilters." They are more exacting than household tap "filters" by removing very fine particles down to 0.4 microns in size. However, they do not trap super-fine particles as well as industrial-grade "ultrafiltration" and "nanofiltration" methods.

Microfilters physically separate protozoa and bacteria from water by pushing water through an internal "filtering media" — a ceramic cartridge or a cluster of hollow-fiber tubes.

These media look solid to the eye, but they contain microscopic pores (typically 0.2 to 0.4 microns) that water can penetrate, but protozoa, cysts and bacteria cannot. Microbiologists call this process "size exclusion." The filtering media basically acts as a microscopic colander that strains bugs out of the water.

Viruses, however, are tiny enough to slip through even these pores. Because the risk of viral contamination in North American wilderness waters is considered low, filters are quite sufficient for most domestic backcountry travel. But in less developed international locales where surface water is exposed to all manner of human and animal activity (such as remote villages, primitive farming communities and heavily concentrated population centers), treating water with a purifier is a must.

What Are Your Choices?

REI offers a variety of water-purification options:


This miniature light saber comes in multiple models. It uses ultraviolet light to deactivate the unseen cooties (viruses included) that could be lurking in water. Short-wave UV light (specifically, UVC, which transmits "germicidal" attributes) zaps, or "disrupts," their DNA, rendering them unable to reproduce and thus cause illness.


  • All SteriPEN models are small, simple to use and lightweight.
  • No wait time is needed once water has been exposed to UV light.
  • UV light imparts no taste to the water.
  • The wand can be used to treat water (without ice) in individual drinking glasses, such as in hotel rooms.
  • UV light is very effective against Cryptosporidium, the most treatment-resistant pest among protozoa and bacteria.


  • The quartz lamp could break.
  • Batteries can run out. (The manufacturer recommends using lithium batteries.)
  • Not effective in very dirty or gritty water unless it is prefiltered or clarified. Light must interact with organisms in order to be effective.


  • If water has a high particulate content, use the SteriPEN's prefilter — a screw-on cap for water bottles equipped with a 4-micron screen.
  • The use of the prefilter is advised in any outdoor situation to keep water as particulate-free as possible.
  • For speed and simplicity, bring a water bottle with threads that are compatible with the prefilter.
  • If the water clarity is poor, give it a second or even a third dosage of UV light.

MSR Sweetwater Purifier System

This uses a 2-step approach: 1) mechanical filtration followed by 2) chemical treatment (drops of a chlorine solution). Some cautious wilderness land managers even advocate this 2-stage process as the most failsafe approach to backcountry water. MSR recommends filtering first, then applying the solution. The company also states that the Sweetwater solution is formulated to be effective only with the Sweetwater's borosilicate filtering medium.


  • Rugged construction is less susceptible to breakage.
  • Needs no batteries.
  • The filtration stage eliminates protozoa, cysts and bacteria; the chemical treatment is required only to deactivate viruses.


  • Requires the physical effort of pumping; some people consider this slow and tiring.
  • Treated water may project a slight chlorine taste.
  • A modest wait time is involved after drops are added — MSR recommends 5 minutes to eliminate viruses.
  • Extra-cautious souls may want to wait up to 30 minutes, particularly if the water is very cold.


  • Avoid wait time for chemical disinfection by prepping water at night for the next day's activity.
  • Remember to take ample Sweetwater solution (packaged in 2-ounce bottles). Or teach yourself how to blend your own replacement solution using diluted liquid bleach.
  • As of this writing, the Transportation Security Administration prohibits pure liquid bleach or pool-strength chlorine in airline luggage. The Sweetwater solution contains 3.5% sodium hypochlorite (bleach, but in a highly diluted state). When traveling with the solution, the smart move, if possible, is to pack it in your checked luggage.

First Need

First Need units feature a proprietary, carbon-treated filtering media, described as an electrostatically charged "structured matrix." Only its manufacturer (General Ecology) fully comprehends what's going on inside the First Need's tangled web of sci-fi fibers. (It's a combination of microfiltration and a process known as "adsorption," which causes suspended matter, such as viruses swimming in water, to adhere to a filtering material, all without chemicals.)


  • All models operate like standard pump filters, and the XL and Base Camp claim a pretty speedy flow rate, roughly 1.9 liters per minute. (One liter per minute is considered a basic flow rate for pump filters.)
  • Can withstand rough handling in luggage.
  • The Trav-L Pure is a self-contained unit (no dangling hoses), but its flow rate is slower.
  • Water is instantly drinkable with all models.
  • With no chemical interaction, no taste is imparted to the water.


  • First Need canisters are not field cleanable.
  • Pre-filters are available, but if you anticipate treating murky, muddy or silt-heavy water, a First Need canister potentially could plug up faster than you would like.
  • After extended use, the ability of a First Need canister to capture viruses gradually diminishes.

Katadyn Exstream

This squeeze bottle is equipped with a replaceable cartridge connected to the straw-like sip tube. When the bottle is squeezed, water is pushed through a 3-stage treatment process: 1) a filter, using pleated glass fiber with 1-micron pores, 2) tiny beads of iodinated resin, to deactivate viruses and 3) carbon molecules, to promote clean-tasting water. It is designed for single-person, on-the-go use, typically day trips only.


  • Very simple and convenient.
  • Water is instantly drinkable.


  • The sip tube produces only a thin stream of water, so don't expect to pour down water in big gulps.
  • Iodine should not be used by pregnant women and people with thyroid conditions.
  • Dirty water could cause the cartridge to clog.
  • Treated water conveys the taste of iodine.

Chemicals (Chlorine Dioxide Tablets)

Chlorine dioxide tablets (found at REI under the brand name Micropur) meet EPA guidelines for effectiveness against harmful waterborne microorganisms, including viruses and hard-shelled Cryptosporidium.


  • Very simple, light, small and convenient. Just drop a tablet in a quart of water and wait.


  • Wait time is usually 30 minutes, but rises to 4 hours if Cryptosporidium is a known risk.
  • Required wait time can frustrate thirsty users.
  • The colder and/or dirtier the water, the longer the recommended dwell time.
  • Some impact on taste may be noticeable.
  • Not an ideal choice for murky or muddy water.
  • Not always effective against Cryptosporidium due to the bug's egg like shell. When crypto is a serious concern (inquire locally), more reliable options are microfilters, UV light or boiling.


  • Avoid wait time for chemical disinfection by prepping water at night for the next day's activity.
  • Iodine is an alternate chemical treatment, but it is not effective against Cryptosporidium It is also not advised for use by people with thyroid conditions or pregnant women.


If no other option is available to you, and you have access to a pan and a heat source, you can always boil the water. Among medical professionals, this process is called "heat disinfection." It is a foolproof treatment method.


  • Effective against all waterborne pathogens. Always.


  • It's less than ideal if you have a limited fuel supply. You must wait for water to cool before you drink it (unless, of course, you're brewing a hot beverage).


  • It is elevated heat, not the specific act of boiling, that kills microorganisms and disinfects water. Nearly all waterborne pathogens are killed within minutes after contact with standard pasteurization temperatures (60°C/131°F, 65°C/149°F and 70°C/158°F).
  • Bringing water to a boil (100°C/212°F) simply provides visual evidence that the water has achieved a microbe-vanquishing temperature.
  • The most heat-resistant bug out there is the virus hepatitis A. Even it is believed to expire in less than 1 minute in water heated to 98°C/208°F. It is because of hepatitis A (or maybe just tradition) that some health organizations and wilderness rangers persist in recommending at least 1 minute of boiling time to purify water, and 3 minutes at higher elevations.

Important: Read the instructions that accompany any water-treatment product you select. Read them carefully, then follow them. For example, do not immediately drink treated water if your chosen method recommends (as several do) a dwell time of between 5 minutes and 4 hours.

Notes on chemical contamination and other urban hazards: Herbicides and pesticides can be absorbed by filters equipped with a carbon element or counteracted by some purifiers that employ a chemical component. With bioterrorism agents, it depends on the size of the organism. Anthrax, MSR Corp. reports, is a bacteria that can range from 1 to 8 microns. Thus it would be captured by all filters carried at REI. High concentrations of chemicals and heavy chemicals, though, cannot be reliably removed by portable filters or purifiers. Always avoid collecting water from water sources near agricultural activity, heavy industry, mines or their nearby tailing ponds.

Notes on product availability: REI's product selection varies from time to time. Any of these products could drop out of our product assortment at any time. Sometimes a particular item REI stocks may be temporarily unavailable due to product issues with individual manufacturers. And new products may be added before we have a chance to update this article. We apologize if any of these circumstances complicates your efforts to acquire the water-treatment system that you prefer.

View the Centers for Disease Control and Prevention (CDC) guidelines for international travel.

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