Water Purification Methods

Sadly, the days of freshly melted snow filling the streams with clean, crisp, and drinkable water are gone. When outdoors it is no longer possible to be sure that water is safe to drink, and thus we have to treat it. At least we have an array of options to choose from – all with their pros and cons.

There are three types of pathogens –  protozoa, bacteria, and viruses – found in water that need to be reduced to a safe number (or eliminated – if possible) before you quench your thirst. The easiest and most effective way to reduce pathogens is by boiling the water, other methods include iodine or chlorine treatment, filtration, or UV light radiation.

What’s in the water?

At higher altitudes a majority of the pathogens found in water that are harmful to ingest come from animal and/or human feces. This is the natural happen stance when water flows from multiple areas into one stream. Be aware though and do your best to support a healthy ecosystem. Always remember to dig you toilet hole at least 200 feet from any water source, and proper hygiene is always your main concern!

At lower altitudes, be aware that chemicals such as pesticides also might be tainting the water source. Therefore, when in doubt, take the necessary precautions.

Pathogens are measured in microns (size). This period mark . is approximately 600 microns. The size of a pathogen will be especially important when looking at filtration systems. Here is a breakdown of common pathogens found in water, their category and size.

  • Organism: Examples, General Size, Filter Type, Particle Size Rating
    • Protozoa: Giardia, Cryptospordium, 5 microns or larger, Water filter, 1.0 to 4.0 microns
    • Bacteria: Cholera, E. coli, Salmonella, 0.2 to 0.5 microns, Microfilter, .02 to 1.0 microns
    • Viruses: Hepatitis A, rotavirus, Norwalk virus, 0.004 microns, Water purifier, to 0.004 microns


Known to be the most effective pathogen reduction method, according to the CDC, killing nearly all pathogens in the water. According to the Wilderness Medical Society, 160 F (70 C) kills all pathogens within 30 minutes, while 185 F (85 C) takes only a few minutes to kill all the pathogens.

According to the CDC, “water should be brought to a roiling boil for 1 minute. At altitudes greater than 6,562 ft. (2000 m) you should boil water for 3 minutes.”

Please note that the boiling temperature of water at sea level is 212 F (100 C). If you bring a pot of water up to a boil and then turn off the heat, it should kill all pathogens. This is because the heat will continue to kill the pathogens until the water reaches bellow 185 F, which should over 1 minute. At higher altitudes, lower the heat for a few more minutes – keeping the water roiling; adding more time the higher your elevation.

Chemical Purification (Iodine & Chlorine)

Both methods are partially effective depending on the water temperature, pH level, water clarity, and other factors. The cloudier the water, the stronger the concentration of chemical required to disinfect. Most pills require 30 minutes of “resting time” before the water is drinkable. The clock starts after the pill(s) is completely dissolved. Always follow the directions on the bottle. Be aware that the colder the water is, the less effective the chemical purification methods are.


Iodine treatments usually come in tablet form that must be kept in dark bottles (light-sensitive) and works best in water over 68 F (21 C). It is more effective than chlorine in inactivation of Giardia cysts, though not effective against Cryporidium (still relatively rare in the USA). Iodine is known to leave an unpleasant aftertaste. It i possible to add another pill to takeaway the taste or to crush vitamin C tablets into your water after the purification process is complete.

Iodine is a necessary part of the human diet, needed to maintain thyroid function. It is found in many common foods, including: cow’s milk, frozen yogurt, and salt water fish. However, ingesting iodine on a regular basis through purification tablets is considered unhealthy (with debates ranging from 6 weeks to 3 months). Though it should be noted that this is a more natural ingredient for the body to ingest than chlorine. Iodine is rapidly metabolized and cleared from the body.

If you suffer from thyroid problems, are pregnant, or are a 50+ year-old women, consult your doctor before you begin use. Also note that some people do suffer from allergic reactions to iodine.


Popular due to its lack of taste (still a little, but less than iodine), Chlorine has a high effectiveness in killing bacteria and viruses, with a low effectiveness at killing giardia. The tablets induce an oxidation reaction that kills the pathogens by breaking down their cell walls. The common tablet “Aqua Mira” (as do most tablet producers) uses chlorine dioxide, a different chemical compound than chlorine.

Compared to iodine, it seems to be a little less effective on the spectrum of pathogens it kills. However, this is widely debated and a personal call. It is popular due to the remnant taste weaker than iodine.

Like iodine, the ingestion of chlorine should be kept as minimal as possible over a duration longer than 6 weeks (debates ranging from 6 weeks to 3 months). Of course, use the necessary amounts to purify the water! Just note possible health effects if taken regularly over a longer duration.


Filtration works by filtering organisms to a certain size (like draining pasta). Depending on the size of the filter, different pathogens may still be able to get through. Check the filter size against common pathogens in the areas you will be trekking. The CDC warns that filters are not effective against all viruses. It is highly recommended to use a filter and iodine or chloride treatment.

There are three main types of filters that come with two different internal systems.

  • Water Filter: protects against most protozoa.
  • Microfilter: protects against most protozoa and bacteria.
  • Water Purifier: protects against most protozoa, bacteria, and viruses.

The two internal systems are either a membrane filter or a depth filter. Also remember that the hose that is placed into the water source needs to be treated like a contaminated object until properly cleaned.

Try to use water from moving sources (e.g., stream or river). If none is available, dip the hose bellow the surface of the lake, but attempt to keep it close to the top where the rays of sunlight would have had time to kill off some pathogens – natural purification at work. If you must filter dirty water, let it stand over night so the larger particles may settle at the bottom, in order to not clog your filter.

UV Light 

UV light destroys the microorganism’s DNA which stops it from being able to reproduce.  The most common product on the market is the SteriPEN ($80-$100), which can filter a water bottle in less than a minute. Be aware that this product works best on relatively clear water. If the water is not clear, either filter first or lay a bandana over your bottle before pouring the water in. The cloth will help catch the larger pieces of debris, but by no means is a filtration system. Rated as a water purifier, the SterniPEN is effective against protozoa, bacteria, and viruses, weighs only 3.6 ounces (SteriPen Adventure Optic), and leaves no after taste.

What Product is Best

This is a highly personal question! There is no correct answer. It depends on your preferences, weight goals (pack weight), amount of available pre-treated drinking water, along with other factors.

Personally, we used the MSR MiniWorks EX Water Filter (protozoa and bacteria) while backpacking along the Appalachian Trail, while Tzachi used iodine and chlorine tablets throughout South America. Currently, we are debating between iodine and filtration or buy a SteriPEN for our trip to Nepal.



This material is based on personal research and readings. Please beware to the pros and cons of all options, along with any personal sensitivities you may have to products or treatments. GrabTheBackpacks is not responsible for the health or safety of any readers, along with any inaccuracies within this article.

Main Sources: OA Guide to Water Purification by Rick Curtis in association with the Outdoor Action Program at Princeton University, the Center for Disease Control, American Thyroid Association, and hikelight.com

2 responses to “Water Purification Methods

  1. We also spent time researching the best filter for our use on our trip around the world and settled on the SteriPen (which we wrote up on our blog). The deciding factor, in the end, was its light weight. Since our trip is so long we’re also taking spare batteries. Here’s hoping it does the job well!

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