Is It Safe? Will My Filter Clean This?

Looking at the above picture, does it look like a safe water hole?

Yes it looks safe, but what you don’t see in the pictures are the cattle off to the left of the picture. Also right behind this field or opposite the road behind me is several agricultural fields where chemicals and pesticides are used.

The cattle endanger this water hole because of the urine and fecal matter that makes its way into the water containing viruses, cryptosporidium and all kinds of nasties. A water filter may help but some may not! Many filters will not filter out chemical contamination. Usually distillation is the only safe way of getting water cleaned and the chemicals removed.

I recently saw a couple hikers stop and fill their water bottles from this pool and instantly thought, man I sure hope they don’t drink that without treating it.. The bad thing is the water looks safe and to the unsuspecting or untrained it could make them horribly sick.

Below are some facts from Outdoor Gear Lab on the types of filters and what they will and will not filter.


Protozoa: This group includes the most commonly feared of all water-borne illnesses – Giardia and Cryptosporidium. These are single-celled parasitic organisms that cause intense intestinal problems, with symptoms appearing anywhere from two days to two weeks from ingestion. These organisms can live in cold water for weeks or months at a time. Cryptosporidium has a hard protective outer layer, which makes it resistant to many types of water treatment.

Bacteria: E. coli, Dysentary and Campylobacteriosis, as just a few examples, can also live in water. These are the easiest pathogens to filter out and treat, since they are much larger than viruses.

Viruses: Examples include Hepatitis A and rotovirus. Viruses are not thought to be a large threat when hiking and traveling in the US and Canada, but on other international trips, viruses become a much larger concern. Viruses are extremely small, so they are not strained out with most filters.

Once you are aware of the risks of water-borne pathogens, the next step is learning how to prevent these illnesses.

Purifiers vs. Filters
Filters and purifiers have technical differences in effectiveness. A filter mechanically pushes water through an actual filter, straining out bacteria and protozoa, but typically does NOT kill viruses. A purifier is a system that is approved for eliminating viruses as well as bacteria and protozoa, and usually involves chemicals, though UV light functions as a purifier as well. An example of a filter would be the Katadyn Hiker Pro, and a purifier would be the Aquamira Water Treatment drops.

What System Works on What Pathogen?
Unfortunately, there is no miracle system that is the perfect solution, though some systems come pretty close. Often times, manufacturers recommend carrying a filter AND a chemical treatment because that is the fastest and most efficient way to eliminate all harmful possibilities from water. Here is our quick and easy breakdown on what types of systems kill what types of pathogens and vice versa:

Effectiveness of Systems:

Filters: Eliminate bacteria and Cryptosporidium, but not viruses. They strain out particulate and usually improve the taste of the water.

Chemical Treatments: Eliminate bacteria and viruses, eliminate Cryptosporidium usually only after extended incubation time, does not strain out particulate, and usually negatively affects the taste of water.

UV Purifiers: Effective against all pathogens: bacteria, viruses, and protozoa. UV treatments do not actually kill pathogens, they simply scramble the DNA of the organisms so that they cannot reproduce. Be careful of treating water and then letting it sit in visible light for a long period of time, because the organisms can reactivate. They do not strain out particulate unless you use a pre-filter. Do not change the taste of the water. One other noteworthy detail is that the EPA approves of the UV process as a purifier, which is used in many large commercial water treatment plants; however, the organization does not actually approve specific UV devices that hikers carry.

What Eliminates Certain Pathogens?

Cryptosporidium: Filters eliminate, UV purifiers effectively disable, chlorine dioxide tablets eliminate after four hours and drops after one hour, iodine does not work.

Viruses: Eliminated by iodine, chlorine dioxide, and UV purifiers, but not filters.

Bacteria: Eliminated by all systems: filters, chemical treatments, and UV purifiers.

Particulate: Okay, so this isn’t a harmful pathogen, but silt and dead bugs do not make for appetizing water. Filters, or separately purchased pre-filters, are the only things that strain particles out of your water.


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