How to Purify Water While on Trail

Having a few purification tablets in your pack provides a great backup in case you need to purify water while you are hiking. The most common pathogens, Giardia and Cryptosporidium, can be filtered out of the water with a filter that has a pore size of 1 micron (0.000001 meter) or less. But viruses can’t be filtered from water because they are too small (about 0.004 to 0.1 microns in width). In the rare cases where you suspect water might be contaminated with viruses, you can treat the water with purification tablets.

muddy water in a pond

Water Sources Vary

It’s impossible to know the condition of any water source without conducting laboratory tests. However, in areas where sewage and other waste can pollute the water supply there is a higher risk of viral pathogens. In these rare cases where you think the water may be contaminated with a virus, you should consider purifying your water with purification tablets.

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.  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.

When using sodium dicholorisocyanurate a slight smell and taste of chlorine was 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.


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.