Is it sufficient to purify drinking water with a small ount of bleach?

I try to keep my backpack light, so for water purification (in Washington’s Cascade Mountains), I carry just a vial of household bleach and use two drops per quart of drinking water. I have never had any problems, but I have a cast iron stomach anyway. What do you think? Doug Tacoma, Washington

Oct 18, 2007
Outside Magazine
Sawyer Water Filter Bottle

Sawyer Water Filter Bottle


Well, Doug, first of all, let me say that you have a simply wonderful first name.

Now, about your question. There are two parts to it. The first is sort of a cloud-seeding question. You say that you have been using household bleach for water purification, and, so far as I can tell from your remarks, you have not become ill from waterborne pathogens or parasites. Correct? My own view is that the odds are good you simply avoided contaminated water. I take precautions (filtering), but I’ve long felt that if you don’t drink from pools of standing water or from streams through heavily camped-in areas, the risks are pretty low. In other words, maybe it would rain even if the cloud was NOT seeded, and maybe you’d have been fine doing nothing. So it’s not easy for me to say, “Yes, what you’re doing is working just fine!"

The other question is this: Is bleach safe and effective? The answer: a qualified yes. Bleach added to water at a rate of two drops per quart is quite safe to drink. It probably doesn’t smell or taste good, but that dissipates if the water is left standing for a while. But provided the treated water is shaken thoroughly and left standing for half an hour, most, if not all, bacteria and viruses will be killed. It isn’t clear, however, that this works against protozoa such as giardia. And it definitely doesn’t eliminate cryptosporidia. Also, you must take care that the water is clean, not turbid or otherwise visibly dirty.

So while you are taking steps to protect yourself, in my view you’re also taking a bit of a risk. My own feeling is that if what you’ve been doing works for you, keeping doing it. But you might also benefit from a personal filter system—a water bottle with a built-in filter. The Sawyer Water Filter Bottle ($55; sawyerproducts.com) is effective against microorganisms.

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