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SteriPEN Adventurer Opti Water Purifier Review

The SteriPEN Adventurer Opti Ultraviolet Water Purifier
The SteriPEN Adventurer Opti Ultraviolet Water Purifier

When the weather gets cold and temperatures drop below freezing at night, I like to switch from using a water filter like the Sawyer Squeeze which will break if frozen (even a bit) to the SteriPEN Adventurer Opti Water Purifier. It works in freezing temperatures, as long as your water is still liquid because it sterilizes Giardia, Cryptosporidia, bacteria, and viruses using ultraviolet light. Later in the winter, when I have to melt snow to get my drinking water, I boil it to purify it. But the SteriPEN is a useful solution for that month before winter and the month before spring when nighttime temperatures still dip below freezing but there’s no snow on the ground or little left.

SteriPEN Adventurer Opti UV Water Purifier

Treatment Capacity
Ease of Use


Compact and lightweight, the SteriPEN Adventurer Opti Water Purifier uses ultraviolet light and an optical eye to purify water, in even the coldest conditions.

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While I have carried a water filter in a zip lock bag in colder weather and slept with it to keep it warm at night, it’s an awkward solution to the frozen water filter problem. The same holds for trying to keep your Aquamira Water Purification Drops from freezing. Carrying a SteriPEN is just easier and more convenient for me, even though I prefer using those water purification methods for the rest of the year. See Cold Weather Water Treatment and Purification for a discussion of the pros and cons of different water treatment solutions in cold weather.

But like all backcountry water treatment solutions, the SteriPEN Adventurer Opti has its PROS and CONS, and is not suitable in all circumstances.

Neutralizes biological organismsDoes not work with all bottles or reservoirs
Very fastBattery dependent
Non-mechanical, no pumpingDoes not remove chemical or mineral contaminents
Effective in cold or freezing weatherNot effective with cloudy or murky water
Does not affect tasteDoes not neutralize larger organisms, i.e. worm eggs

It works for me because I usually purify very clear water from mountain streams that are free from the chemical pollutants you find near agricultural or urban areas.

The Adventurer Opti weighs 3.6 oz including batteries and can purify 50 liters of water. That’s more than enough for the 1-2 night backpacking trips I take after the weather’s gotten cooler, even if I’m hiking with companions. In temperatures under 32 degrees, SteriPEN recommends wearing the Adventure Opti close to your skin to keep it warm. I hang it from a lanyard around my neck and it’s lightweight enough that I soon forget about it. SteriPEN used to make an even lighter weight model, the Freedom (2.6 oz), but it’s been discontinued.

The SteriPEN Adventurer Opti can be used to purify 1 liter or half-liter of water at a time. You can use it with any plastic, metal, ceramic or glass bottle as long as it has a wide enough opening so you can submerge the Opti’s light element in it. While a wide-mouth 1 liter Nalgene bottle is very convenient to use, there’s no reason you can’t use a cooking pot too. Once submerged, you stir the water gently with the SteriPEN until the UV light goes off, which signals that your water is purified. It takes about 90 seconds to finish. Before drinking, wipe the threads of your bottle with a clean cloth if they’re wet since the SteriPEN’s light can’t reach them. This isn’t a big concern since your immune system can usually handle the small number of organisms remaining on the threads if any.

The Adventurer Opti is powered by two CR123 lithium batteries, which are relatively inexpensive if you buy them in quantity at Amazon. They’re lithium batteries so they’re good in cold weather and won’t freeze when the temperature drops below 32 degrees, like alkaline batteries that contain water. If you take longer trips, the SteriPEN Classic or SteriPEN Aqua might be a better solution because they can purify 150 liters on a single set of AA batteries, although both are about twice as heavy as the Adventurer Opti, with batteries.

Like all water treatment solutions, it’s important to carry a backup if your primary method fails. In cold weather, I switch from Aquamira Chlorine Dioxide Water Purification Drops to Katadyn Micropur Chlorine Dioxide Tablets because the latter are unaffected by being frozen. They have a longer treatment time than the SteriPEN, particularly in colder water, which is why I use them a backup and not my primary cold weather purification method.

Disclosure: The author purchased this product with his own funds.

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One comment

  1. Good review most others fail to mention it won’t kill tiny little swimming bugs or the threads issue.
    Regarding the threads being dried that makes me nervous, I bring a light disposable type bottle to collect water and small funnel to get the water into my wide mouth bottle. Then transfer and steripen it. No thread issues just bit more gear to carry.

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