Water Purification in the Backcountry

• Biologically contaminated water contains infection-causing microorganisms such as Giardia, bacteria, or viruses.

• Chemically contaminated water contains hazardous levels of chemicals from pesticide runoff, mine tailings, naturally occurring mineral deposits, secretions from blue-green algae, etc.

• Boiling, filtering, or chemically treating water can remove or kill microorganisms, but it will not remove chemical toxins.

Biologically vs Chemically Contaminated Water

Boiling• Boiling is the most certain way of killing all

microorganisms. • According to the Wilderness Medical Society,

water temperatures above 160° F kill all pathogens within 30 minutes and above 185° F within a few minutes.

• Generally, in the time it takes for the water to reach the boiling point (212° F) from 185° F, all pathogens will be killed.

• To be extra safe, let the water boil rapidly for one minute, especially at higher altitudes since water boils at a lower temperature

Boiling Temperature vs Altitude

Chemical Treatment with Chlorine or Iodine

• Effective against protozoans (Giardia), bacteria and viruses

• Follow label directions, watch expiration dates• Low temps = increased waiting time• Turbidity (high solids) reduces effectiveness

(use cloth strainer or coffee filter)• Don’t add drink mix until treatment

is complete

Chemical Treatment with Chlorine or Iodine

• Small and light – good back-up• Keep hands away from eyes after handling

tablets• Tip: swish water to dissolve tablets. Start

timing after tablet dissolves completely• Tip: After tablet dissolves, splash some of the

water on the threads and cap

Iodine

• Some don’t like taste• Best if water > 68oF• Contraindications:

Women over 50Iodine allergy (shellfish??)PregnantThyroid problemsLithium treatment

Chlorine

• Micropur MP1 tablets issued at Philmont• Generally no allergy problems• Effective when used correctly, but not idiot-

proof

Katadyn Micropur MP1 Chemical Tablets

Microorganisms Killed Contact Time

 EPA Water #1(clear, 68º F)

EPA Water #2(dirty, 39º F)

Bacteria 15 Minutes 15 Minutes

Virus 15 Minutes 15 Minutes

Cysts 30 Minutes 4 Hours

Filtration

Water Filters• Effective against protozoans (Giardia) and

bacteria. • NOT effective against viruses (viruses are too

small). Waterborne viruses are generally not considered an issue in North American backcountry waters.

• Work on turbid (high solids) water, but filters clog more quickly.

• Work on cold waterE. coli

Working Parts of a Filter

Water Filter Strategies and Tips• Two people per filter is fastest. One pumps while the

other holds the receiving bottles and manages the lids• Choose the clearest water available. Calm water from

a large lake is best.• Draw water from below the surface and above the

bottom.• Let turbid water settle first, or prefilter w/ cloth, a

coffee filter or an inline filter

MSR Sweetwater Siltstopper Inline Prefilter

Water Filter Cleaning & Maintenance

• Some filter elements can be cleaned to restore flow, others must be replaced

• Some tolerate freezing, others don’t• Read the directions and practice!• Keep the dirty hose separate from the clean

hose. Don’t mix them up.• Clean and dry hoses after trips (same goes for

hydration systems)

Variations on the Filter Theme• Structured matrix or filter plus built-in chemical

treatment for viruses (meet EPA “purifier” tests)• Gravity Filters – no pump, so slow, but good for camp• Squeeze filters – generate pressure by squeezing a

bag or bottle • Straws – generate pressure by mouth suction

UV Purification• Good for protozoans

(Giardia), bacteria and viruses

• Not good for turbid (high solids) water

• Works in cold water. • Requires batteries• Bulb delicate??