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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 or the Katadyn BeFREE (3L) which 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 sterilises 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 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’s 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 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 cook 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.

Written 2017.

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

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  1. I love the reviews that say “carry a backup”. What is the backup? Chlorine dioxide, which never breaks. So just carry that.

    It works in 15 minutes in “EPA 1” water (non-cloudy, room temperature) and two hours in “EPA 2” water (cloudy, near freezing).

  2. Walter, the only times I contracted gardia was when I was using chlorine-dioxide. 15 minutes doesn’t do the job on all water.

    Using the Steripen year round saves a LOT of water weight. From around 2-4L I dropped to 1 liter…a little more than 2-4 pounds. Backups? A set of ten tablets will get me out of the woods in most cases, and, there is always boiling. Ease of use, speedy (<45 sec wait time), no back flushing a clogged filter, highly effective treatment, the weight savings of not carrying extra "cooking" water, and, the lack of sensitivity to water temperature all make the Steripen my first choice for drinking water in the ADK's. A pair of new batteries will usually do enough water for two people for week of steady hiking.

    • Ditto what James said. Chlorine dioxide works too slowly in cold water to be a primary method unless you want to carry extra water. I need an extra liter to cover the two hour wait times which is 2 extra pounds. Carrying a few tablets will get you out of the woods though in your primary breaks. I’ve had water filters die in the woods and having a backup is prudent.

  3. How does the SteriPEN Adventurer compare to the SteriPEN Ultra? Is it just the difference in battery?

    • Yes, basically. All the lamps are pretty much the same using the same voltage and have the same life expectancy. Only the Aqua model is less, but I am not sure why.

  4. Mt daughter spent a year working for an NGO in Uganda, where you need to be cautious about your water. I armed her with a Sawyer Mini and a Steripen. The one removed particulate matter as well as the tiny bugs, the other sterilized the water. It was an effective system and her colleagues wound up having Steripens sent to Uganda.

  5. Thanks for the review! I do a lot of day hiking and trail running in the cold temps and I haven’t had to sterilize any water during them – yet. I hadn’t really thought about the effect of freezing temperatures on my filter or the tablets. Looks like I will be replacing the steri pen my dog ate a few years ago!

  6. Opinions seem to vary, but tend toward caution, on the question of whether melted-but-not-boiled snow water is microbially safe to drink. I’ve read that ice is more likely to harbor Bad Small Things than snow. But any precipitation starts its life by water vapor condensing around a small particle (a nucleus, in the jargon). These can be just about anything, including whatever viruses, bacteria, cysts, spores, etc. that may be coursing through the atmosphere. So, the cautious assumption is that snow could contain some microbial stuff you might not want to ingest.

    Bringing snow melt to a rolling boil solves the problem, but if one is conserving fuel, an alternative would be bringing the snow melt to a moderate temperature, then treating with the uv pen.

  7. I use cr123 re-chargeable batteries. In near freezing or below freezing temps the pen won’t work as the batteries need to be warmed up. I usually put them under my arm pits for 3-4 mins and that does the trick. Plus I carry an extra pair of batteries just in case. After the comments I read here, I will carry tablets as a backup from now on.

  8. Philip, nice review. I’ve used a Steripen on my Annual JMT hikes for 5 of them or more. I find a $5 1/2 micron water scoop/pre-filter is great and it only weighs 1 oz for scooping up the water into the container you use to sterilize the water. This filter can be washed in a laundromat on your zero day and it also serves to expedite the wait time if you use Chlorine Dioxide tablets (since it takes care of parasites, you only need to wait 15 minutes then). http://www.dudadiesel.com/choose_item.php?id=PTFEP3S — I use when I get the filters in the mail, a wire cutter and needle nose pliers to remove the wire rim at the top, bringing the filter down to 1 oz and enabling it to be folded up and stored in a quart ziplock freezer bag. Many backpackers order this exact filter and it’s been popular a long time at backpackinglight.com. About half of the hikers who hike with me annually use this same filter. When I scoop up the water, I count to about 2 seconds to have any contaminated water on the outside drip off and then the water coming through the scoop then first has to go through the pre-filter.

  9. I have the Ultra, which you can also has a clever collar on it allowing you to push it up against a narrow bottle (like a platypus or bottled water), invert it, and swirl it around. I love it, though I did have to have my first one replaced after the indicator screen stopped working.

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