Filtering protocol: how strict should I be about dirty water contaminating my clean water?

[Rafi Harzahav]

Hi, Everyone.

Well, I know that variants of this issue has been addressed in the past, but I'll ask my own version:

I use a Sawyer squeeze filter for my backpacking trips. For convenience, a tornado tube is used to connect the filter output with a clean water bottle. When I'm done filtering, I screw caps onto the filter input and output as well as the dirty water bottles (evernew) and throw all this into a pocket in the backpack. I generally don't put any unused clean water bottle or the tornado tube in the same pocket. Now, I suppose there is no real risk of contamination of the unused clean bottle if I screw its cap on securely, but I'm still reluctant to throw my tornado tube in with the rest of the stuff. This is out of concern that the tornado tube may come into contact with dirty water on the outside of the filter or the outside of a dirty water bottle. Are these concerns unfounded? Are a few drops of dirty water on the tornado tube any cause for worry?

Thanks!

rhz

[Bob Gross]

There is relatively little risk with your method. However, that is not exactly zero point zero risk.

I take an ordinary grocery store produce bag, and I cut it down to the dimensions that I need. I can use that small bag to cover the raw water items, or I can use it to cover the clean water items, but not both at once with the same bag. The bag has negligible weight.

Personally, I use a gravity filter, so I have one end of its hoses that is in contact with raw water. Sometimes I will place that in the top of my backpack where it will dry out quickly. The clean water parts are still attached, but elsewhere.

–B.G.–

[Kevin Gurney]

I try to avoid the worry by keeping my "dirty" items (scoop, funnel w/prefilter, dirty water bag) in a separate ditty from my clean items (Sawyer, tubing). And then keep those two ditties on opposite sides of my pack, with the dirty stuff next to my fuel and cat hole kit. Basically, there's nothing in that pocket I want to put into my mouth!

When collecting water I try not to get unfiltered water on my hands and then touch my clean water items. But of course that happens from time to time, so I first completely sterilize my hands by wiping them on my dusty pants and all is well. :)

I guess we do our best to keep the dirty and clean away from each other and hope for the best. And if we do get sick, we post a long rant here about that damned filter that didn't keep us safe!

[Jerry Adams]

There are 500 drops in an ounce. If you had a 20 ounce water bottle that would be 10,000 drops.

If you had one drop of dirty water in with your clean water, that would be 99.99% clean. EPA requirement is 99.9999% (for bacteria), so you wouldn't meet that, but that's pretty conservative.

If you're going to filter, you may as well try to keep all dirty water out of the clean water.

If a clean got contaminated, you could rinse it out a few times with filtered water and that would probably do it. But there might be some little crevice that didn't get rinsed out.

[Bob Gross]

Jerry, are you mostly worried about bacteria?

I am more concerned about parasitic cysts, like Giardia lamblia.

I guess it depends on where your raw water comes from.

–B.G.–

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