Travel Reference
In-Depth Information
Filtration
Watercanbecompletelyclearedbyfiltration.Filtersusedfordisinfectingwaterperform
this function well but do become obstructed. A filter that can be manually cleaned is es-
sential. For large groups, a large-volume filter such as the Katadyn® Explorer (1 gal/min)
servesquitewell.Thefiltercanberemovedinseconds,andscrubbingitfortwentyorthirty
seconds with a brush or scrubber gets rid of the obstruction. (At least one Grand Canyon
rafting company uses a battery-operated electric filter.) Usually two to three liters can be
filtered before cleaning is necessary. The one- or two-person smaller filters, such as the
Sweetwater filter, also clear water and can be easily cleaned, but they can filter only about
one liter between cleanings.
Flocculation
Flocculation wasusedtoremoveunpleasantcolors,smells,andtastesfromwaterbythe
Egyptians as long ago as
BC
2000. Currently it is widely used in municipal water plants,
andthetechniquecanbeappliedinthefield,althoughitistimeconsumingandrarelyused.
Flocculation removes suspended matter—colloids—that are not settled by gravity, which
includesorganicandinorganicmaterialandmanymicroorganisms,includingmorethan90
percent of
Giardia
cysts and most bacteria and viruses. However, it does not remove all
microorganisms and must be followed by a second step, such as halogenation or heat.
The best flocculant is alum (aluminum potassium sulfate), a common chemical used by
the food industry in baking powder and for pickling. It can be found in food stores or in
chemical supply houses. Other substances, such as lime or potash, can act as flocculants.
Baking powder or even the fine white ash from a campfire can be used in an emergency.
The alum induces colloid particles to coagulate, forming larger clumps that settle by
gravity or layer on top. Approximately one-eighth to one-quarter of a teaspoon of alum per
gallonshouldbeaddedtowaterandmixedwellandfrequentlyforfiveminutes.(Thealum
does not need to be measured precisely.) The mixture should be allowed to settle for thirty
tosixtyminutes,thendecantedorfilteredthroughacoffeefilterorafinemeshcloth.Since
alum is nontoxic, if the water is not cleared by the first flocculation, the process can be re-
peated a second or third time.
Granular Activated Charcoal
Granular activated charcoal binds (adsorbs) many chemicals to its surface. It is used
widely in medicine to treat poisoning or overdose by binding toxins in the intestines. This
nonspecific adsorption also removes chemicals from water. Charcoal filters/purifiers for
householdusearepopularforremovingthetasteandsmellofchlorinationby-productsand
toxic chemical contaminants such as pesticides. Several field devices combine filtration
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