Geoscience Reference
In-Depth Information
“purifying” filters have iodine-impregnated resin beads in the filter media, which release iodine
into the water to kill viruses and bacteria. These chemically active resins require sufficiently
warm water temperatures and relatively long contact times to kill bacteria and viruses. Some
lab tests indicate that most or all iodine-based purifiers may not pass the EPA “purifier” stand-
ard without pumping water through the device more than once or at extremely slow flow rates
(Vorhis 1997, 13). If viral contamination is a big concern, I personally would not trust the iod-
ine resin in my purifying filter, but would pretreat the water with a chemical treatment before
running it through my filter to remove protozoan cysts and the bad taste of the chemicals, or
zap it with UV sterilization from a “Steripen” after I had filtered it to clarify the water and re-
move bad tastes and harmful chemicals. There is one certified purifying filter, the First Need
Deluxe Purifier, which uses no iodine to remove bacteria and viruses, and is not as prone to the
temperature, flow rate, and usage factors that might allow viruses to slip through most other
purifiers, but if your water supply is dirty, it will clog this filter in short order.
If you do use a certified “purifying” water filter on dirty water, like a duck pond or urban
stream, without secondary chemical treatment, I would be extra careful to run the water
through the filters at a
very slow rate
and suggest
running the water through the filter twice
.
Katadyn, First Need, Berkey, and Sweetwater make certified “purifying” filters, which cost on
the order of $40 to $130, and have fairly low capacities (about 10 to 20 gallons if you are treat-
ing reasonably clear, clean water).
Ceramic Versus Carbon Cartridge Filters
If you might be using your backcountry water filter a lot, I would recommend that you pur-
chase a filter with a ceramic filter element, like the Katadyn or MSR units. These units offer far
longer life at a much lower cost per filtered gallon than carbon-based or pleated-membrane fil-
ter elements. All filter elements have clogging problems that will severely reduce their capacity
(useful life), if used with dirty water. Ceramic cartridges will clog faster than the other types of
cartridges, but can be serviced fairly easily by scrubbing the outer clogging layer with a scrub-
bing pad that is supplied with the filter to restore the filter to near its original performance.
Some filters have replaceable pre-filters, which help somewhat with clogging, but since the
pore size of the pre-filter is usually much larger than the pore size of the main filter, small
particles tend to slip through the pre-filter and continue to clog the main filter. Backwashing
capabilities can also help extend filter life. A lot of people swear by the backcountry water fil-
ters with pleated membranes and carbon block cores, like the Katadyn Hiker Pro or the MSR
Sweetwater, which pump water faster and easier than the filters with ceramic-type cartridges
