Water from natural sources like streams, rivers, and springs should never be consumed without treatment. The misconception that flowing water is inherently pure or “self-purifying” poses a health risk. Even in remote areas, water sources are subject to contamination that cannot be seen, smelled, or tasted. The appearance of clear, cold water often misleads people, but visual assessment is an unreliable indicator of potability.
The Illusion of Safety in Flowing Water
The belief that rapid movement cleanses water is an illusion based on the physical appearance of the stream. Clarity means the water is low in suspended sediment, which offers no guarantee against microscopic threats. Fast currents may dilute contaminants, but they do not eliminate them. The rapid flow can actually keep harmful microorganisms suspended throughout the water column.
A stream’s water quality is determined by everything that happens upstream, often miles away. Contamination frequently comes from non-point sources, such as agricultural runoff carrying animal waste or pesticides. Wildlife like deer, beaver, and birds also introduce fecal matter, even in pristine wilderness environments. Human activity, including poorly managed septic systems or waste from recreational campsites, adds further risk to the water source.
Invisible Biological and Chemical Contaminants
The danger lies in the three primary classes of biological contaminants shed in human and animal feces. Bacteria, such as Escherichia coli (E. coli) and Salmonella, are single-celled organisms that cause immediate, severe gastrointestinal illnesses. Protozoa, like Giardia lamblia and Cryptosporidium parvum, form hardy cysts highly resistant to some chemical disinfectants. Ingesting these organisms can lead to prolonged diarrhea and abdominal cramps.
Viruses, although less common in remote backcountry water, are the smallest biological threat and can cause illnesses like Norovirus and Hepatitis A. Moving water can also carry chemical contaminants from upstream sources. Agricultural and urban runoff introduce pesticides and heavy metals, while discarded plastics break down into suspended microplastics. These chemical pollutants often pass through basic water filters, posing long-term health risks that simple disinfection cannot resolve.
Essential Water Treatment Methods
To ensure safety, a multi-barrier approach combining filtration and disinfection is the most reliable method for treating natural water sources. The simplest way to eliminate all biological threats, including bacteria, protozoa, and viruses, is by boiling the water. At elevations up to 6,500 feet, a one-minute rolling boil is sufficient to inactivate all pathogens. Above 6,500 feet, where water boils at a lower temperature, the water should be held at a rolling boil for three minutes.
Mechanical Filtration
Portable water filters are rated by the size of the pores in their media, measured in microns. Filters rated 0.5 microns or less are necessary to physically block larger protozoan cysts like Giardia and Cryptosporidium. While these filters effectively remove bacteria and cysts, they are generally not small enough to block waterborne viruses. For virus removal, a specialized water purifier utilizing a chemical matrix or a filter with a pore size of 0.01 to 0.02 microns is required.
Chemical Disinfection
Chemical treatment is a lightweight and convenient option, often using iodine or chlorine dioxide to disinfect the water. Iodine is effective against many bacteria and viruses, but it is not reliable for inactivating Cryptosporidium oocysts. Chlorine dioxide is a superior disinfectant that can eliminate Cryptosporidium, but it requires a longer contact time, sometimes up to four hours. Regardless of the method used, pre-filtering cloudy water to remove sediment is important. Suspended particles can shield microorganisms from the disinfectant or clog the filter prematurely.