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cross-contamination while using water filter

I thought of you-all this weekend. I was backpacking in the Sierra and had a little "accident". I've read here about the cross-contamination issue when using a water filter. And this one was a doozie.

I stopped by a nice little stream which was obviously the headquarters for mosquito breeding for all of California (at least). It was also clear they had all just been released from an over-eaters anonymous therapy session, and weren't about to lose any time making up for their lost meals.

Anyway, I used my Miniworks EX to fill my 3L MSR bladder. I had the filter screwed onto the bladder using the conveniently-sized mouth on the bladder. Anyone who has used a Miniworks EX realizes filling a vessel this size, particularly while bathing in hungry mosquitoes, takes a while.

Just as I finished, I lifted the bladder + filter up ... and was about to unscrew the filter. Then ........ SPLASH!!! the bladder gratuitously detached itself from the filter and want splashing into the stream.

I wasn't about to risk using it at that point. Undoubtedly some of the "clean" water was displaced in the fall and replaced by untreated water. I emptied out the bladder in disgust and packed it away.

Fortunately I wasn't counting on that as my only water storage...

arrrgh! :)

So today I splashed around lots of dish washing detergent in the bladder and ran it through the tube for a while before vigorously rinsing the whole thing. Hopefully all the little giardiasis critters and all their friends are gone...

Ah yes nothing like the west side Sierras for mosquitoes, except Wisconsin, or the South, or Alaska, or most of Canada or about everywhere except the desert!

First the good news. If you do an internet search for Sierra water quality you will be pleased to find the vast majority of high Sierra venues DO NOT warrant bringing a filter/sterilizing system. One of these studies points out most of the contamination present in the Sierra mountain waters is also present at even greater concentration in city tap water. And the key to most domestic water borne illness usually is determined by how many of these critters populate your guts. If you ingest a fairly contaminated source, the starting number of breeders has a better chance of blooming to unhealthy levels than if you ingested a source with few of the critters swimming around. Thus the reason why we don’t get ill drinking city water – the critters are flushed from our guts before they have time to multiply into a critical mass. There are however, specific locations these study do advise using filtration or sterilization. As one study summarized, what these locations all share is high to excessive human presence, and frequent to heavy livestock and livery presence. Based on my familiarity with some of the suspect locations, they are among the busiest of all Sierra venues, and as a body comprise less than 5% of the backcountry. More good news: the seasonal cold cycle kills off living bugs, so every season starts over with minimal contamination, regarding the undesirable microbes. Thus even known contaminated locations may be benign early in the season. So you probably have no need to worry about your blivet or filter being tainted.

But if your blivet or filter were contaminated, detergent is not a disinfectant; you need something strong that kills the critters such as bleach. So if you still feel the need to be for sure for sure, give your kit a second going over, this time using enough bleach to taint the wash water with a strong chlorine scent.


Hmmm, thanks for the info. I guess I find it hard to trust the water in the Sierra given how crowded it is, especially around where this incident occurred. But your comments regarding the various surveys are somewhat reassuring.

Meanwhile, I figured using the detergent wouldn't necessarily "kill" the little buggers, but might wash 'em away.

Between that, and your explanation about the relatively safety of the water in the Sierra, I guess I'll take my chances and see if I get sick after using the water bladder on my next trip :).

Hmmm, thanks for the info. I guess I find it hard to trust the water in the Sierra given how crowded it is, especially around where this incident occurred...

I have lost my links to the water surveys, but they are ongoing and updated yearly. You can find these reports searching the internet. These studies are conducted by both government agencies, as well as reputable universities. Some include lists of sites surveyed, along with meterics on the data collected.

Thanks - I'll check that out.

Bleach, about 1-2 drops per liter is enough to disenfect. Some people even use this method to treat the water they drink.

The only other option really is to put it in direct sunlight and let it dry. Waterborne bacteria etc can not survive 1)UV radiation 2) being dry.

That is why filters that use a ceramic filter like the Miniworks EX dont have your sterilize the filter, but just have you air dry it.

I could just go look it up, but does the miniworks use silver in the ceramic as well?
(Replying via droid)

No, it doesn't only the kat pocket filter has silver, which basically just means that it doesn't have to be dried after every use neccesarily. Silver just inhibits bacteria growth. I usually dry my miniworks every night when I get to camp.

Actually I noticed the other day that the instructions for the Miniworks EX suggest boiling the filter to sterilize it if it's been used for more than 7 consecutive days, and/or after long-term storage (esp if stored wet).

Bheiser1, yes that is true if it is stored wet. But that's why I let it dry every evening after I use it. Anything if stored wet will/can grow nasties, well except for the kat pocket with the silver


In many years of my outdoor use of Katadyn water filters (I am their Northern-Rockies representative) there have been occasional cross-contamination incidents.

Stuff happens, and I can be clumsy at times. However these incidents always have involved splashing or immersing an external part of filters in possibly contaminated water.

An engineer friend assured me: “dilution is the solution.” We repeatedly rinse the contaminated area in filtered water.

I think your soap & water, and repeated rinses, plus drying have likely cleaned out your 3 Liter bladder.

For cleaning the large internal area of your bladder, I would not recommend chlorine bleach per this link to The Center for Disease Control. “Many species of Cryptosporidium exist that infect humans and a wide range of animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine disinfection.”

However chlorine dioxide is more reactive than chlorine and has been proven to kill Cryptosporidium in rigorous testing at EPA approved labs. You can buy chlorine dioxide tablets from Katadyn under the brand name Micropur, or from Wisconsin Pharmical under the brand name Potable Aqua Chlorine Dioxide Tablets. MSR Miox produces the same 4 PPM concentration of Chlorine Dioxide as the tablets.

In clean 68 degree water, the Micropur tablets kill Cryptosporidium (and every other tested micro-organism) within 30 minutes in a 1 tablet to 1 Liter of water concentration. In 38 degree, slightly acidic, sewer water: kill time goes to 4 hours.

September 27, 2020
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