Equipment: Water purification in the field

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I'm off this summer for 6 weeks of trekking across the Silk Road in China. I think it'll be an experience of a lifetime -- and an opportunity to take some great photographs. But that's not what I want to blog about today. Today's topic is: Purity of Essence .... errr... water (in a Strangelovian sense)

That is, in the nether reaches of the world, you're not always guaranteed to have fresh water. Even in Beijing and Shanghai, you're warned not to use the water from the hotel taps for drinking -- instead, boiled water in thermoses or spring water in sealed PET bottles is provided.

When I went to my travel doctor for the usual pre-travel battery of injections (HPA, HPB, DtP, tentanus, and influenza), he also recommended that I think about purity of water as well, since Western China is still developing. The main fears that I have about water are:

  • Viruses: Hepatitis (even with vaccination, it's best to avoid exposure)
  • Parasites: cryptosporadia and other protozoa, etc.
  • Bacteria of all sorts
  • Industrial pollutants: pesticides, heavy metals

When hiking in the American backcountry, I've usually relied on iodine tablets such as Potable Aqua or my little MSR filter. But my MSR filter (which didn't work against viruses such as Hepatitis) was lost in the Black Hole of Moving and Iodine doesn't work against Cryptosporadia. My doctor recommended chlorine dioxide tablets, but I noticed that it would take 4 hours of treatment before they killed all the little buggers.

Being a gadget-girl, I couldn't fail to notice the latest high-tech weapons race against ailments of the stomach and liver. (more after the jump)

Here are the various pros and few of the cons of water purifiers and filters:

Iodine tablets
(Potable Aqua)
1l per 15 min (per tablet)Dirt cheap, very portableDoesn't kill protozoa
Taste/color. Run out of tablets, run out of treatment.
$5 for 30 tablets
Chlorine dioxide tablets
(Katadyn Micropur)
1 l per 15 min (viruses)
1 l per 4 hours (protozoa) (per tablet)
Cheap, very portable4 hours to kill protozoa. Run out of tablets, run out of treatment.
$14 for 30 tablets
Pump filter
(Sweetwater Guardian)
1.25l per minInexpensiveBulky. Have to clean filters. Ones without iodine resin filters do not all catch viruses.$60-100
Water bottle filter
(Katadyn Extream)
0.3l per minInexpensive. Compact. Has iodine filter for viruses.Have to clean filters. Limited capacity (0.3 liters/minute). New filter costs almost as much as the new kit ($40)$40-60
(MSR Miox)
1 l per 15 min (viruses)
1 l per 4 hours (protozoa)
Compact. Very sturdy.Expensive. Relies on batteries (2 x CR123). 4 hours to kill parasites$130
UV Light
1l per 80 secondsCompact. Very fast. Kills everything.Expensive. Relies on batteries (Aquastar: 2 x CR-123A; SurPen = 4 x AA). Glass tube can break$100-150

(Note: For Americans: 1 liter is approximately 1 quart)

What I was mainly concerned about was purifying water in hotel rooms and public restaurants or on public transportation. In that context, chlorine dioxide or iodine tablets take too long. While they are great for base camps where you need a lot of water for cooking, I couldn't see using a manual pump in a bouncy bus or in a street market. The water-bottle filter seemed like a good option. But they have limited capacity and the filter price racks up over time.

The most elegant solution seems to be the UV lights which use a short burst of irradiation in the UV-C spectrum to disintegrate the DNA of microorganisms and viruses. They require about 30 seconds of treatment for 1 liter of water. There are two products on the market for travellers: The SteriPen and the AquaStar. More on them in the next blog entry.


I found that clean drinking water in plastic bottles was very widely available on the Silk Road in Western China , certainly anyplace where there were buses and markets (e.g., Urumqi, Turfan, Kashgar, all the oasis cities of the Tarim basin and around the rim of the Taklamakan). I didn't go to the trouble of purifying my own water, but relied on the ability to purchase it. I made a point to wash my hands a lot, peel my own fruit (bring a pocket knife) and I never got sick. Carry a Nalgene bottle to bring drinking water from your base of operations -- it gets *very* hot in the summer. Ironically, the places where I've been struck by GI worries have been while staying in fancy hotels in Shanghai and Hong Kong.

Don't miss the spectacular Sunday market in Kashgar -- bring your camera, trade your camel or buy a sheep! The fruit in Xinjiang (melon from Hami) is luscious, and if you hanker for a real cup of coffee and a brownie, try the Caravan Cafe in Kashgar next to the Chinibagh -- it's run by an expat ethno-musicologist from Wisconsin, who now makes his home in Kashgar with his wife and daughters. Practice your Uighyr, as
Mandarin will limit your ability to connect with the local folks. This area is a major crossroads for the peoples of Central Asia.

The chlorine dioxide tablets are great. Look Especially for Aseptrol(TM) made by Engelhard Corporation. (May be marketed under other names.)

An excellent reference on chlorine dioxide is: Geo. Clifford White's The Handbook of Chlorination and Alternative Disinfectants, 4th Ed., Chapter 12. (Available from WWW.AWWA.ORG)

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About this Entry

This page contains a single entry by Karen Nakamura published on May 9, 2006 8:03 AM.

Info: More LED geekiness was the previous entry in this blog.

Careers: Tips for new faculty from OSU is the next entry in this blog.

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