What’s the difference between a backpacking water filter and water purifier?
Simply put, the main difference lies in the level of protection they provide. Generally speaking, a water filter is designed to remove waterborne protozoa and bacteria, but not viruses. A water purifier is designed to combat all three classes of microbes, including viruses.
Why the two treatment device options? The main reason is, viruses are just too small for filters to catch. Far smaller than protozoa or bacteria, viruses slip through the technologies used in backpacking filters. Traditionally, UV light, chemical purification treatments or boiling were required to deactivate viruses by scrambling their DNA or killing them. Today, new advancements in mechanical pump purifiers provide a convenient option to physically remove viruses quickly and easily.
When should I use a filter?
If you’re traveling in the backcountries of the U.S. and Canada, a water filter, or more accurately a “microfilter,” is considered sufficient protection. In these pristine landscapes, where human traffic is relatively low, protozoa (like cryptosporidium and giardia), and bacteria (like E. coli and salmonella) are considered the main threats. Waterborne viruses that are harmful to humans are transferred primarily through human waste. Therefore, where human traffic is lower, we assume the risk of viruses to be lower as well.
It’s important to ensure that your microfilter is built to handle backcountry water qualities. Some filters on the market are designed to remove only unpleasant tastes from tap water. Backcountry-grade microfilters remove contaminants down to 0.2 microns and should meet the U.S. EPA’s Guide Standard and Protocol for Testing Microbiological Purifiers (for removal of bacteria and protozoa) or the NSF protocol p231. Learn more about filter testing standards here.
When should I use a purifier?
If you’re traveling to less-developed countries, where water treatment and sanitation infrastructure is poor and/or people don’t practice good hygiene near water supplies, a water purifier is the safer option. A microfilter plus a purifying agent, like chemical tablets, is also a robust option. Common viruses to be aware of include norovirus and hepatitis A.
It’s important to remember that while chemical treatments, UV light and boiling will deactivate the microbes, they won’t rid the water of particles. Particulate in the water can impede the effectiveness of UV light and to a lesser degree, chemicals. Mechanical pump purifiers offer a big advantage in this way, because they aren’t hindered by dirt or sediment in the water.
Mechanical pump purifiers should physically remove contaminants down to 0.02 microns. And all purifiers should meet the same testing standards listed above but for all three classes of microbes.
Three scenarios to consider:
Backpacking in Washington’s North Cascades National Park:
You’ll be collecting water from subalpine streams and lakes along established hiking trails during the summer. Any pathogenic risks in the water will come from humans and animals, but are usually light in concentration. Here, bacteria and protozoa are the primary threats; the likelihood of encountering viruses is very low. The water may also contain particulate like dirt or sediment, which will need to be removed.
Treatment choice: A microfilter — with one note of caution from MSR microbiologist Zac Gleason: “As more and more people get out with less and less education or regard for others, viruses will become more of an issue. Lakes where people swim are already resulting in more and more norovirus outbreaks.”
Camping on a holiday weekend at very popular lowland lake:
You’ll be collecting water from the lake, the shores of which are packed with campers. The higher concentration of humans leads to a higher risk of viruses. The water also contains particulates, which you’ll want to remove.
Treatment choice: A mechanical pump purifier, or microfilter plus purifying agent
Hotel stay in Huaraz, Peru, before hiking into the Cordillera Blanca Mountains.
At the hotel, you’ll be collecting water from the tap. Potential pathogens will come from humans and animals, carried to your faucet through a suspect water treatment system. Here, bacteria, protozoa and viruses are all of concern. However, the water is completely clear, free of particulates.
Treatment choice: A pump purifier, UV light or a chemical treatment