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Posted by Bill S on October 22, 2007 at 1:54:39 pm EDT
In reply to Water purification in extreme conditions posted by Bill S on October 19, 2007 at 11:58:04 am EDT

Hujambo, Alan (I'm trying to learn some Swahili, but that's most of my current vocabulary) -

Red Cross and other international agencies are using reverse osmosis systems that are too bulky for our trip, and the system that Alicia mentioned. That PuR system was developed by PuR in conjunction with Proctor and Gamble as a way of getting inexpensive purified water on a small scale for organizations like UN agencies, Red Cross, etc. We are looking into whether it is available to private individuals at this point (the literature that Dave and Alicia and I picked up at the OR Show seemed to indicate that it won't be available for individuals for a few more months).

The other approach used has been to let the water settle for a while, decant the clearer stuff, then boil the water. I have done that sort of thing when canoeing or kayaking on the lower Colorado River, but it leaves pretty murky-looking water (never got sick from it, though).

The prefilter is good, to a point. I think the Sweetwater pre-filter (which I have, with several refills) may be ok to put on one of my pump filters to keep them from clogging. But I have found (as previously noted) that coffee filters and the standard bandana or "clean cotton cloth" just take out the big stuff. Even a commercial filter bag (0.5 micron) made by a company a friend works for leaves my test mixture output looking too murky for a Steripen, and it leaves it requiring at least a double treatment from Miox (part of the Miox kit is indicator paper that should turn purple after treatment is complete).

Reverse osmosis is also a way of desalinating water, so units are available for sailboats and much used by the ocean racers, even for those crazy folks who sail solo in the Drake Passage. But the smallest of them in my neighborhood West Marine are much too bulky for even checked baggage on the plane.

I won't have a problem when up on the mountain, since the mountain streams are pretty clear. It's just when out on the Serengeti and similar places where we have a few days where we have to share the waterholes with the "Big Five" and their smaller cousins.

By the way, as I have been reviewing treatment methods, I was reminded that, while iodine requires a half hour (relatively clear water at 20C or above), chlorine dioxide, the big current favorite among backpackers, requires 4 hours away from sunlight(!) to fully react (again, relatively clear water, 20C or above).

The backpacker-type pumps will work. It's just the clogging problem. The backpacker pumps with a carbon final element (the Katadyn filter bottle, for example, or the Sweetwater, or any pump with the Katadyn carbon post-filter) will remove some heavy metals and some organics (which means pesticides or fertilizers), but the manufacturers won't give any numbers on how effective they are for this, unlike their numbers for the tiny critters.

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