Chemical Purification of Fresh Water

Luckiamute Falls

Our packs are packed, kayaks and fishing gear ready, and our camping supplies are always ready. It’s not only in case we have to evacuate, but also to take planned or unplanned trips.  Part of those supplies include water purification systems.

While we won’t swim where we know we can’t drink the water, it is nice to know that should public water sources not be available, we can still enjoy the great outdoors.  Even during a world changing event, being prepared for the worst will make camping with our family and friends seem less traumatic and stressful for everyone.  Distillation is our preferred water purification method, having the proper water purification chemicals will go a long way towards providing peace and security if you can’t use your stove.

If you plan to use freshwater sources not part of a public water supply, be sure to contact your local fish and game department or department of state parks to find out which lakes and rivers are closed to swimming or fishing.  Chances are you won’t want to use the water for drinking either.  Some times part of a lake is closed due to algae blooms or other reasons.

It is impossible to tell by looking if water is contaminated. Water purification tablets can be used as a last resort, for a few days, when other methods are not available. Chemical purification systems are used to kill bacteria and viruses in drinking water, especially giardia and cryptosporidium. Use chemical purification tablets when no other method is available and for no longer than five days.

The two chemicals most people choose are:

  • Chlorine dioxide tablets (or droplets)
  • Iodine tablets (or droplets)

These chemicals are cheap to purchase and light weight to carry in a pocket or backpack.

Choosing the freshwater source:

Water should be moving, as in a stream or river.  Or, in the case of lakes or ponds, examine it carefully.  If a lake or pond might be unsuitable in one location, try another location.  The larger the body of water, the more likely at least some part of it will be suitable for chemical purification.

Never use water from any source with dead fish or animals, any odor coming from the water, and algae blooms. The water must not be stagnant nor have a foamy surface. These waters may not be suitable for chemical purification systems.

How to use chemical purification systems:

Follow package instructions at all times.  Failure to follow the instructions exactly as listed could lead to severe illness or death.

Pour clear water into your container.  If you have to use muddy water, strain through fabric until it runs clear.   Add chemicals according to package instructions. For maximum effectiveness, the ideal water temperature is 80ºF. If using chlorine dioxide, wait at least four hours, longer at temperatures below 62ºF. When using iodine, use a dark container and do not use under 68ºF, wait 30 minutes. Chemical purification is completely ineffective near 35ºF.

Pros and cons of  each chemical system:

Chlorine dioxide is most effective against cryptosporidium. The municipal water taste dissipates when left open for an additional 30 minutes.

Iodine does not kill cryptosporidium, and leaves a foul taste to be neutralized with vitamin C.

Women over 50 and persons with certain allergies and health conditions should not use iodine.  Consult your physician for your situation.

Iodine has a long shelf life.

Shelf life of products:

Chlorine dioxide has a long shelf life. Once opened, chlorine dioxide tablets lose potency within a few days. Visually examine previously opened tablets before use. Gray or brown discolored tablets may retain some effectiveness. Tablets with a green or yellow discoloration should not be used. Some brands of chlorine dioxide tablets are packed in waterproof foil sheets.

Store chemical purification systems under controlled temperatures between 68°F and 86°F. Protect them from light or replace yearly. Check with the manufacturer for information about how the production date is displayed on the package before purchase.


photo by: Ian Sane