What is a micron and why should you care when filtering water?

On long backcountry treks, you’ll want a hydration plan other than to lug around multiple gallons of water. When you encounter a freshwater source, such as a river or a lake, you have a few options to make that water potable: boil, filter or treat with tablets.

You’ll want to treat the water, no matter how clean it looks. It could have bacteria, viruses and parasites that can make you sick. Boiling the water for a full minute at a rolling boil should kill most of those nasty organisms. At elevations of 6,500 feet and above, boil for three minutes.

If you’re on the go, though, you can drop water treatment tablets into your bottle and wait a half-hour for clean water. Or you could filter your H2O — but what kind of filter should you use? There are straws, pumps, bags and bottles. Some contain chemicals or carbon to further treat the water. Many companies tout how small their filter pores are, using a measurement called microns. So, what is a micron?

Micron is short for micrometer, which is one-millionth of a meter. For those of us not too familiar with the metric system, especially the minuscule end of it, a micron equals .00003937 inches.

Seems like that should be small enough to stop most contaminants, right? Well, yes, for sand, dirt, protozoan cysts, most bacteria and the diarrhea-inducing parasite Cryptosporidium, which measures at about 5 microns. However, some viruses can be as small as .0004 microns in size.

Viruses likely won’t be much of a risk when traveling in the backcountry, so a filter with pores 1 micron or less should provide sufficient protection. Most microfilters measure at .2 microns. Consider investing in a water purifier instead if you’re traveling in places where people are being unhygienic around water sources. Or again, go with the tablets or boiling your water.

Another label to take notice of is “absolute pore size” and “mean pore size.” “Absolute” refers to the largest pore in the filter, while “mean” is the average, meaning there are pore sizes bigger and smaller.

Filters to check out

If you’re in the market for a water filter or purifier for your next outdoor adventure, check the list of a few below, some of them are available at the Scout Shop:

Filter reviews

To see some of the filters and other water treatment products in action, the Scout Life staff has reviewed some. See the videos below: