Downsizing Water Purification Treatments

If I want to purify just 8 ounces of water instead of the recommended one liter or quart, can I just use a smaller amount of the recommended treatment dosage?

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With chemical water purification tablets, almost all of them give instructions for a full quart or liter. If I want to clean just 8 ounces, could I divide the dose by breaking tablets into quarters (or cut the number of drops by 1/4), and would the treatments still be effective?

Submitted by – Jeremy, from the Get Out More Tour


When I first received this question, I was intrigued, because in the 15 years that I’ve been answering reader queries, I hadn’t heard it. So I sought the help of some chemical experts, who confirmed that it is NOT a good idea to split dosages (more on why, below).

But as I thought about it more, I realized, that even if the answer was “Yes, you can safely divide tablets or drops to treat smaller amounts,” it still doesn’t make sense to do so. Why would you only want to treat 8 ounces of water on a hike? It’s like eating a single M&M. You’ll eventually need that water, so treat a whole bottle and share it or save it for later. Plus, chemicals require up to four hours to be effective, and if you’re hiking hard, you should drink more than that amount in that time frame.

OK, enough preaching. Maybe you have a perfectly reasonable explanation for wanting to treat only 8 measly ounces at a time. But you shouldn’t, according to Brian Roche of McNett, the makers of Aquamira. “As a general rule we would not recommend going against the instructions on the packaging for the drops or tabs,” he says. “It’s safest to treat water one quart at a time. And while increasing the dose for larger quantities of water is easy, it’s just too risky to recommend that consumers use less treatment for smaller amounts of water. It’s hard to get an exact measurement on the container for the correct amount of Aquamira to add.

Bill Bussler of Wisconsin Pharmacal, maker of Potable Aqua tablets, agrees. “It’s actually very difficult to cut one of the tablets exactly in half. So, the concentration of available iodine in the water might not be enough to treat the water, which poses a potential health risk,” he says. But since it takes two PA tabs to treat a liter, you could treat a half liter with just one tablet, he says.