How to Purify Water While on Trail

You should have some purification tablets in your pack. This provides a great backup in case you need to purify water while you are hiking. If you experience contaminated water it is likely from Giardia and Cryptosporidium. A water filter that has a pore size of 1 micron (0.000001 meter) or less can filter these pathogens. But you can’t filter out viruses from water because they are too small (about 0.004 to 0.1 microns in width). You might find suspect water likely contaminated with viruses. In these cases you can chemically treat this water with purification tablets.

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muddy water in a pond

Water Sources Vary

It’s impossible to know the true condition of any water source without conducting laboratory tests. However, in areas where sewage and other waste can pollute the water there is a higher risk of viral pathogens. In these cases you should have purification tablets so you can safely treat the water.

water molecule

Sodium Dichloroisocyanurate

Sodium Dichloroisocyanurate is the active ingredient in some water purification tablets. This chemical compound slowly releases chlorine at a relatively constant rate. As a result of the chlorine viruses and pathogens can’t survive.  One tablet (50 mg) in 0.75 liters reaches a chlorine concentration of about 7 ppm after about 30 minutes. This concentration of chlorine safely treats water from ponds, lakes, wells, cisterns, and similar water sources.

If you use sodium dicholorisocyanurate a slight smell and taste of chlorine might be detected.

aqua tabs being weighed on a scale

Purification tablets are easy to carry

The Sodium Dichloroisocyanurate tablets weigh about 50 milligrams each. Ten purification tablets with the protective packaging weighs 1.4 grams. Ten purification tablets will be capable of purifying 7.5 liters of water. Because of the light weight and effectiveness of purification tablets I recommend carrying at least 4 tablets.


Most backcountry water sources can be made safe to drink by filtration alone. However, in rare cases you might experience water that is contaminated with viral pathogens. If you suspect the water source is contaminated with a viral pathogen then purifying the water is the safest solution.

When purifying water, always follow the directions provided by the manufacturer.