Submissions     Contact     Advertise     Donate     BlogRoll     Subscribe                         

Tuesday, February 22, 2011

Methods of Water Purification

boiling waterYou can go for 3 days without water.

Effectiveness of different water purification methods.
Data gathered from various sources.

Contamination.. Iodine..Chlorine..Filter #1...Filter #2...Filter #3...Boiling
Giardia ................Fair.... Fair....... Fair..... Good .....Good..... Good
Cryptosporidiosis.. Fair... ..Fair....... Fair..... Good..... Good..... Good
Viruses............... Good.. Good...... Poor..... Poor..... Good..... Good
Taste of water after
purification.......... Bad.... Bad........ Good.... Good.... Good..... Good

Filter #1 = Reverse Osmosis Filter

Filter #2 = Absolute 1 micron filters

Filter #3 = Nominal 1 micron filters


Regular bleach (for laundry use) usually has about 4% to 6% available chlorine. Check the chlorine content before using, and add according
to the following guidelines:

1% chlorine (10-20 drops / litre)
4% to 6% chlorine (2-4 drops / litre)
7% to 10% chlorine (1-2 drops / litre)

Water should stand after treatment for 30 - 60 minutes. If water is murky or very cold, the treatment time should be lengthened
to several hours over even overnight.

Boiling Water -- A rolling boil of one minute at 7000 ft or lower.
A rolling boil of two minutes 7000 ft to 11,000 ft.
A rolling boil of three minutes above 11,000 ft.

Iodine (Polar Pure) About $12.95 will get you 90 days supply. It comes with a thermometer because dosage is temperature dependent.

Unpurified drinking water may contain four things that pose health risks: protozoan parasites (e.g. giardia), toxic bacteria, viruses, and poisonous chemicals. Only boiling and iodine are entirely effective against the first three, and only charcoal filtration is effective against the fourth.

Just ten years ago, halazone tablets were the preferred water treatment method. Even today, many commercial rafting companies use Clorox(TM) to disinfect dishes. Both halazone and Clorox are chlorine-based, and because chlorine is unstable, slow to disinfect, and pH-sensitive, it is not always effective against protozoa and viruses. Halazone also tastes worse than iodine, so there's no excuse for using it. US municipal water supplies are usually treated with chlorine, so your tap water may not always be free of micro-organisms.

The First Need(R) water filter is cheap (less than $40), but is effective only against protozoan parasites. Its .4 micron filter pores are smaller than giardia cysts (3.5 microns), but larger than some bacteria. The marketing brochure for the First Need says it removes 99% of cholera and typhoid bacteria, but does not say that E. coli bacteria (which range from .3 to .9 microns) go right through its screen. A few years ago my wife got a case of turista on a Deschutes trip where we filtered all our water through a First Need. (The banks of the Deschutes are heavily grazed, and cattle are prime carriers of E. coli.) The bacteria remained in the filter and she got the same case of turista the next few times we used the filter, until we bought a new one. If you own a First Need, flush it with iodine as soon as you come home. The First Need's charcoal canister is not big enough to be effective against poisonous chemicals -- you need a pound of charcoal for this -- so the charcoal just adds unnecessary weight, and provides a potential haven for the growth of harmful bacteria.

The Katadyn(R) pocket water filter is expensive (around $180), but is completely effective against bacteria as well as giardia. Furthermore, it can be cleaned after it clogs up. When our second First Need clogged up (they lasted only one season for us) we bought a Katadyn. The Katadyn is effective at removing smaller bacteria such as E. coli. However, the Katadyn's .2 micron filter is not effective against viruses. If you travel abroad (to Nepal for example), you risk viral infections such as Hepatitis A and Hepatitis non-A non-B, among others. In the US, most water is not yet contaminated by virus, but there's no reason to believe water supplies will remain uncontaminated for much longer.

To be entirely safe, water should be boiled for at least five minutes. Giardia is killed in less than a minute at 176 degrees, well under the boiling point. Bacteria and viruses last somewhat longer, but are probably killed in less than five minutes at 190 degrees. Some viruses may last longer; nobody knows. At 10,000 feet water boils at 194 degrees, so above this altitude you should boil water an extra minute for each 1000 feet. Very few river trips start this high, however. The main problem with boiling water is that it requires lots of fuel, which may be at a premium on long river trips.

If you have neither the time nor the inclination to boil water, iodine is equally effective. After 10 minutes (20 minutes for very cold water), a sufficient dose of iodine kills all protozoa, bacteria, and viruses. There are many iodination methods, and two excellent ones are commercially available. For low-volume purification, PolarPure(TM) is the best product. After adding water to a bottle containing iodine crystals, you pour a few capfuls into a liter of water and wait 10 minutes. The drawback is that a bottle of PolarPure can purify only 8-10 liters at once. The advantage is that iodine crystals are inert and last a very long time. For high-volume purification, check out Potable-Aqua(TM) tablets. Dissolve one or two tablets in a liter of water and wait 10 minutes. The main problem with iodine tablets is that they degrade upon contact with moisture, so be careful with that bottle, and throw away open bottles when returning home.

An older method, using tincture of iodine, is definitely not a good idea. Tincture contains more sodium iodide than iodine, and because sodium iodide has no disinfectant activity, it unnecessarily increases total iodine consumption.

Although iodine is not highly toxic, continuous ingestion of iodine may cause health problems. A study of Florida prison inmates who consumed iodinated water showed that their pre-existing thyroid conditions got worse. Also, if pregnant women ingest large amounts of iodine, the fetus may get a goiter that could cause respiratory obstruction at birth. The moral of the story is: don't iodinate all your water for more than a few months. The accepted concentration for iodine disinfection is 8 milligrams per liter, but this is mostly to get rid of protozoan parasites. A good compromise would be to filter first, then use a low concentration of iodine to get rid of bacteria and viruses. For this, a concentration of .5 mg/L is deemed adequate, so one capful of PolarPure or one Potable-Aqua tablet should disinfect around 16 liters.

Giardia has become a well-known, almost fashionable, outdoor hazard. Many people who experience gastro-intestinal problems after drinking bad water think they have contracted giardia. In many cases they have contracted something else. Since the only FDA-approved treatment for giardia (Flagyl) is carcinogenic, it's wise to make sure you really have giardia before taking Flagyl. Most low-grade bacterial infections go away on their own, and Flagyl is ineffective against viral infections. Tinidazol may also be available in your are, and is more effective against giardia.

Boiling Water

Boiling water is the best method for making water safe to drink. Boiling water as recommended will kill bacterial, parasitic, and viral causes of diarrhea. Adding a pinch of salt to each quart will improve the taste.

Directions for Boiling Water

Boil water vigorously for 1 minute and allow it to cool to room temperature (do not add ice).
At altitudes greater than 6,562 feet (>2,000 m), boil water for 3 minutes or use chemical disinfection after water has been boiled for 1 minute.

Chemical Disinfection

If boiling water is not possible, chemical disinfection with iodine (e.g., Globaline, Potable-Aqua, or Coghlan’s, found in pharmacies and sporting goods stores) is another method for making water safer to drink. Cryptosporidium (a parasite that can cause diarrhea) and other coccidian parasites (e.g., Cyclospora, Toxoplasma) might not be killed by this method. Cloudy water should be strained through a clean cloth into a container to remove any sediment or floating matter, and then the water should be treated with iodine.

Directions for disinfecting water with iodine

Iodine tablets

Follow the tablet manufacturers' instructions.
If water is cloudy, double the number of tablets.
If water is extremely cold, less than 5° C (41° F), an attempt should be made to warm the water, and the recommended contact time (standing time between adding a chemical disinfectant to the water and drinking the water) should be increased to achieve reliable disinfection.
Note: be sure the tablet size is correct for a Liter of water.

Tincture of Iodine - measure out your dose to water.

If using tincture of iodine 2% solution, add 5 drops to a Liter or Quart of clear water. If the water is cloudy, add 10 drops per Liter or Quart. (Note: 20 drops=1 ml.)
Allow the water to stand for 30 minutes before drinking when the water temperature is at least 25°C (77°F). Increase the standing time for colder water: (e.g., for each 10° less than 25°C (77°F), allow the water to stand for double the time before drinking it.
Crystalline Iodine (found at some chemical companies and sporting goods stores) First make a saturated solution and then measure your own dose to add to water. The crystalline form stores well indefinitely and new batches of the saturated solution can be made from a small amount of crystals each time you take a trip.

To prepare a stock of Crystalline Iodine saturated solution:

Place 4-8 grams of crystalline iodine into a 1-2 oz container and fill with water. Note: 1oz=6 teaspoons.
Warning: crystalline iodine at 4-8 grams is a lethal dose if accidentally swallowed in a single dose. Keep out of the reach of children.
Shake the bottle vigorously for 1 minute. Allow several additional minutes for the iodine to maximally dissolve in the available water. Some crystals should always be visible; if they totally dissolve, then more crystals should be added to the container to insure that iodine saturation of the stock solution has been achieved.
If the water to be treated is clear, add 13 ml of saturated iodine solution -- liquid above the crystals, not the crystals themselves -- per Liter or Quart. Note: 5 ml= 1 teaspoon. 13 ml = about 2.5 teaspoons
In cloudy water, add 26 ml of saturated solution per Liter or Quart.
Note: Allow the solution to stand 20 minutes before drinking the disinfected water when the water temperature is 20-25°C (68-77°F). Increase the standing time with colder water. For each 10° less than 25°C (77°F), allow the water to stand for double the time before drinking.

Portable Water Filters

Certain types of portable water filters can also remove some types of infectious agents from drinking water. However, most of the portable filters on the market do not effectively remove viruses, thus chemical disinfection of water is needed after filtering with such filters to make the water safer for drinking. Some portable water filters designed to remove parasites (Giardia/Cryptosporidium) have an "absolute” pore sizes of 0.1 to 1-micrometer and, therefore, may also remove most diarrhea-causing bacteria. See the Division of Parasitic Diseases' Guide to Water Filters and Bottled Water to learn about different filters and those that filter Cryptosporidium. Viruses are smaller than 0.1 micron and will NOT be removed by filters with a pore size of 0.1 or larger. To kill viruses that may pass through these filters, add iodine (as described above) to the filtered water before you drink it.

Note: Chlorine in various forms has also been used for chemical disinfection. However, it is not as reliable as iodine for killing disease causing organisms in the wide range of water-quality conditions that travelers might encounter


Crystalline iodine 4-8 grams used in a stock solution constitutes a human lethal dose if accidentally swallowed in a single dose. Keep out of the reach of children.
Water that has been disinfected with iodine is NOT recommended for pregnant women, people with thyroid problems, those with known hypersensitivity to iodine, or continuous use for more than a few weeks at a time.

Enhanced by Zemanta

1 comment:

  1. Did you test a Berkey filter? Take a gander at the table at this site, and you'll see that the Berkey filters are far superior to everything else.

    No, I don't sell Berkeys, nor does anyone I know. It just IS better. Note that Berkey doesn't use a micron rating system, due to how easily such a rating can be manipulated - but its Black Berkey elements will remove 99.9999999% of pathogens (not a typo). Here's a FAQ, in which is an explanation of why they don't use a micron rating: