Water filtration or purification is an extremely important skill for preppers. But it is an area in which I see a lot of confusion. There are many different systems that are available and all of them claim to be the best. So let’s review some facts about water filtration and purification that will help you to determine which filters you need.
There are three main processes for water filtration or purification, they are chemical, ultraviolet light or filtration. Today we are going to discuss the various options.
Filters – Filtration occurs when you force water through a filter that removes bacteria and parasites like cryptosporidium and giardia. The filters are effective against bacteria and parasites, but are not normally effective against viruses. When you look at a filtration system, look at the micron size. This is a measurement of the pore size in the filter. The smaller the pore size, the more pathogens the filter can strain out. A simple rule is that the smallest bacteria is 0.2 microns, so a filter should be around that size or smaller to be the most effective.
One thing to check when purchasing a filter is it field serviceable, this means that you can service it on your own in the backcountry if it gets clogged. For example, ceramic filters need to be scraped relatively often, but this is easy to do. Most other filters are designed to be easy to back-flush to remove clogs, but check to see how complicated this process is.
Chemical Treatments: Eliminate bacteria and viruses, but some brands take as long as four hours to eliminate Cryptosporidium. They do not strain out debris, and usually give the water a bad taste.
UV Purifiers are effective against all pathogens including bacteria, viruses, and protozoa. Because UV treatments do not actually kill pathogens, (they simply scramble the DNA of the organisms so that they cannot reproduce) be careful of treating water and then letting it sit in visible light for a long period of time, pathogens can reactivate. UV filters do not strain out particulate or change the taste of the water. The downside of UV purifiers is that they are dependent on batteries to function.
The effects of the various water filtration and purification systems.
Cryptosporidium: A good quality filter can effectively eliminate it. UV purifiers effectively disable it. Chlorine dioxide tablets eliminate cryptosporidium after four hours of exposure, drops take one hour, and iodine does not work.
Viruses: can be eliminated by iodine, chlorine dioxide, and UV purifiers, but not filters.
Bacteria: Eliminated by all systems including filters, chemical treatments, and UV purifiers.
The absolute safest way is to use a combination of chemical and water filtration. However, in the United States one system will be effective in most cases. Currently there is little danger from viruses in water in the US. If you are traveling internationally, you want something that will kill viruses.
We have not discussed boiling water and Sodis, but here is a link to information on Sodis an inexpensive method of water purification and I will discuss boiling water in the near future