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Ultimate SteriPEN Review: Options, Instructions, and How It Compares to Other Purifiers

steripen review

Whether backpacking in the wilderness or in developing countries, a good water purifier is one of the best gear to bring.  Having a water purifier means that you don’t ever have to buy bottled water (and contribute to plastic waste).  Nor do you have to worry about lugging heavy bottles of water up mountains when you can just drink directly from streams.  There are a lot of different purifiers, but SteriPEN is one of the best options.

In this SteriPEN review, I’ll go over everything you need to know about SteriPEN including how it works, how to use SteriPEN, the different types of SteriPEN, and some good alternatives to SteriPEN.


What Is SteriPEN?

SteriPEN classic purifying water with UV light

SteriPEN is a type of water purifier that uses ultraviolet (UV) light to deactivate harmful pathogens in water.  The keyword here is deactivate. Unlike water filters, the SteriPEN doesn’t actually remove the pathogens.  You can buy the SteriPEN here.

Instead the UV light damages the DNA of the pathogens and makes it impossible for them to reproduce.  If the pathogen cannot reproduce, it cannot cause infection.

Fun fact: UV light can even kill bacteria and viruses in the air.  One theory as to why we get sick more in winter is because there isn’t as much UV light from the sun to kill airborne pathogens. (1, 2, 3, 4)

No squeezingRequires batteries
Very fast and easyDon't treat large organisms like worm eggs
Treats viruses as well as bacteria and protozoaWon't remove sediment, chemicals, bad tastes, or smells
Fairly lightweightUV bulb fairly fragile
Good for travel abroad and hikingNot effective on cloudy water


What Does SteriPEN Treat?

SteriPEN uses a UV intensity of 254nm, which is very effective at treating pathogens in water.  When used correctly, it will treat 99.9% of the following pathogens:

  • Bacteria: Including Campylobacter, E. Coli, Salmonella, and Shigella
  • Protozoa: Including Giardia and Cryptosporidium
  • Viruses: Including rotovirus and hepatitis


SteriPEN Does NOT Treat:

  • Chemicals or toxins: Such as fertilizers, pesticides, or chemical runoff.
  • Larger organisms: Such as tapeworm eggs.
  • Cloudy water: The UV light won’t be able to get to the pathogens if the water is murky.


What does this mean for real-life use?

Travel in Undeveloped Countries:

You can use SteriPEN on tap water in underdeveloped countries.  However, it’s not going to be completely effective if the water might be contaminated by chemicals, such as near agricultural or mining areas.

You don’t ever want to drink chemicals, but a few days’ worth of exposure probably isn’t going to give you cancer.  On the plus side, chemicals don’t cause traveler’s diarrhea like bacteria, protozoa, and viruses do, so using SteriPEN will spare you that terrible ordeal!


Backcountry Water:

With backcountry water, things get a bit more complex.  It used to be that you could just use a water filter in the backcountry.  However, viruses are becoming more common in backcountry water because of overcrowding and people going to the bathroom near water sources (follow Leave No Trace, people!!!).

SteriPEN will purify bacteria, parasites, and viruses, but it won’t remove those parasites like tapeworm eggs.  So, you wouldn’t want to rely on SteriPEN alone when drinking from streams, lakes, rivers, or private wells.  You’ll have to get a filter which can remove viruses too (which has it’s drawbacks) or use SteriPEN in addition to a water filter.


How to Use SteriPEN

steripen instructions

Using SteriPEN is really simple.  However, it’s really important that you use it correctly.  Otherwise the UV light won’t be able to reach all the pathogens in the water.

  1. Only use on clear water: Some of the SteriPEN products can be used with cloudy water, but not anything very dark. You need the water to be like a light lemonade.  If the water is murky, then you’ll need to pre-filter it.
  2. Determine how much water you are purifying: Either ½ or 1 liter of water.
  3. Remove lamp cover and click: Use 1 click for ½ liter and 2 clicks for 1 liter of water.
  4. Put the lamp into the water: Depending on the model you have, a green light might flash after you click. Put the lamp wand into the water while it is flashing.  Once the lamp detects water, it will emit UV light.
  5. Stir until the lamp turns off: It’s important that you stir. This agitates the water and ensures all pathogens make it into the UV light.  When the lamp turns off, you are done.  It takes 48 seconds to purify ½ liter of water and 90 seconds for one liter.



  1. It’s really important that you agitate the water while using the SteriPEN. One independent study found that SteriPEN only treated 94.98% of spores when the water wasn’t agitated.
  2. The pre-filter sold by SteriPEN is only 40 microns. That’s enough to remove sediment and make the water look clear so it can be treated by the SteriPEN UV light. However, it is not small enough to remove tapeworm eggs and other parasite eggs.  You can see a list of parasite egg sizes here. Play it safe: I’d recommend using a pre-filter with an absolute rating of at most 1 micron.


Isn’t UV Light Bad for Humans?

Yes, UV light can be very dangerous for humans.  However, SteriPEN is usually used in water bottles.  The plastic, glass, or metal will block the UV light.   If you are using the SteriPEN in a large pot though, some of the UV light could get to your eyes and cause damage.

One cool thing is that SteriPEN only turns on if it detects water.  This feature makes it impossible for you to accidentally blast yourself with UV light.


SteriPEN Comparison

There are several versions of SteriPEN out.  In my opinion, the SteriPEN Ultra (get it here) is the best version because it can be recharged via USB. I typically bring a lightweight power bank on my backpacking trips, which is enough to recharge my devices, headlamps, and a SteriPEN.  On longer trips, you can bring a portable solar panel.

 BatteriesLiters of Water Treated Per Battery/ChargeWeightUse on Cloudy Water?
SteriPEN Classic4 AA batteries100 (with 2,300 NiMH batteries)6.3ozNo
SteriPEN UltraInternal USB-rechargeable lithium-ion505ozNo
SteriPEN Ultralight2 CR123204.8ozNo
SteriPEN Adventurer Opti2 CR123503.6ozYes



SteriPEN vs. Other Water Treatment Systems

Let me start by saying that no water treatment system is perfect.   There’s always going to be a tradeoff.  For example, water filters which can remove viruses are usually reallllly slow and clog easily.  Systems which can remove chemicals require expensive cartridges which have to be changed frequently.

If you are dealing with really dangerous water – viruses and chemicals in addition to the standard bacteria and protozoa – then you will likely need to combine two water treatment methods.

ProductTreats/RemovesTime/Flow RateLifespanWeightPrice Per Liter Treated
SteriPEN UltraBacteria
1 liter/90 seconds8,000 liters5oz$
Sawyer MiniBacteria
0.5-1 liter/minute100,000 gallons2oz$
GRAYL GeoPressBacteria
Heavy metals
Bad tastes and odors
5 liters/minute65 gallons per cartridge15.9oz$$$$$
MSR GuardianBacteria
2.5 liters/minute10,000+ liters17.3oz$$
Katydyn Hiker ProBacteria
Bad tastes
1 liter/minute200 gallons per cartridge11oz$$$
15 minutes-4 hours1 tablet/liter1-2oz per 50 tabs$-$$$$$


Sawyer Mini

tips for sawyer mini

For a long time, Sawyer Mini was my go-to water filter for backpacking.  It is incredibly lightweight.  It’s also very cheap and its filter lasts forever, so there’s not even any cost for replacement filters.

As you would probably expect with such a cheap water filter, there are plenty of downsides.  The main ones are that the Sawyer Mini doesn’t treat viruses (though Sawyer does now make the Point Zero Two filter which can remove viruses, it just gets clogged super easily).

Viruses usually aren’t a problem in backcountry because they don’t survive well in water and UV light from the sun usually will kill them.  However, thanks to overcrowding and irresponsible hikers going to the bathroom close to water sources, viral outbreaks are now becoming common on popular trails (my uncle, for example, is one of many people who succumbed to rotovirus while hiking the AT).

The other downside of the Sawyer Mini is that it takes forever to filter.  I personally don’t mind this, but it can be a pain in the butt if you are in a hurry or need to filter a lot of water at once.  You can buy the Sawyer Mini here.


LifeStraw vs. SteriPEN

The LifeStraw water filter might look cool, but it’s completely impractical to use in real life.  I’ve ranted about this in my post Why I Hate the LifeStraw Water Filter so won’t get into it here.


GRAYL GeoPress vs. SteriPEN

The GRAYL GeoPress is a newer water filter to hit the scene.  It uses a press action instead of pumping, so it is easier to use than most filters.  It also has a carbon filter, which means it can remove chemicals as well as bad odors.

The GRAYL GeoPress would be the very best water purifier, except for one issue: The carbon cartridges don’t last very long.  You’ll have to replace them after 65 gallons, or even more frequently if the water is exceptionally contaminated.  This means the cost adds up much more than most other water filters or the SteriPEN.  It breaks down to about $0.38 per gallon plus the initial cost of the filter. You can get the GRAYL GeoPress here.


MSR Guardian vs. SteriPEN

Long considered one of the best water filters, the MSR Guardian boats impressive features like being able to filter water quickly (5 liters per minute) and having a self-cleaning.  You never have to scrub the filter or back-clean the Guardian!

Because the Guardian filter has a pore size of 0.02 microns, it is able to remove viruses.  This means it can do everything that the SteriPEN does, and it does it without relying on batteries.  The filter cartridge lasts 10,000+ liters, so it really outshines the SteriPEN (as well as most other backpacking filters) in ever way.  The only issue?  It’s a very expensive initial investment. Over time, the investment pays off though since the filter lasts so long.  You can get the MSR Guardian here.


Katadyn Hiker Pro vs. SteriPEN

The Katadyn Hiker Pro is a pump-type water filter.  It’s got a nice big hand pump, so is fairly easy to use.  I also like that it has a tube that goes into the water so you don’t have to crouch right into the water source.

Compared to the SteriPEN, the main advantage of the Hiker Pro filter is that it has a charcoal filter element to remove some bad odors, tastes, and some chemicals.  However, the Hiker Pro won’t treat viruses like the SteriPEN does.  The Hiker Pro also has a fairly short cartridge life of just 200 gallons (less if the water is really murky).  That ends up being around $0.23 per gallon plus the initial cost of the filter.  So the SteriPEN ends up being a much better value over the long run.  Get the Katadyn Hiker Pro filter here.


Water Purification Tablets vs. SteriPEN

Water purification tablets contain chemicals like iodine.  You just drop them in the water and wait.  The chemicals will kill or deactivate pathogens in the water.  Like with the SteriPEN, tablets won’t remove sediment, bad taste, or chemicals.  The main advantage to the SteriPEN vs iodine tablets is that the SteriPEN is much faster.  Some tablets take over 30 minutes to treat viruses.  Also note that many purification tablets don’t treat Cryptosporidium.


The Bottom Line?

The SteriPEN is a great way to treat unsafe tap water when traveling abroad. However, it has a lot of drawbacks for wilderness backpacking – particularly that it doesn’t work on murky water, won’t remove sediment or worm eggs, and relies on batteries.

If you want to use SteriPEN in the backcountry, I’d recommend using it along with a cheap filter like the Sawyer Mini.  The filter takes care of sediment and large parasites.  The SteriPEN then destroys viruses.

If you’d rather only use one purifier, then get yourself the MSR Guardian filter. It’s expensive but lasts almost forever and handles everything except chemicals.  Or, if you want one purifier that can truly do it all – including get rid of chemicals — go with the GRAYL Geopress.  Just be prepared to pay more over the long run since you need to replace the cartridges so frequently.


Image credits:
Sanitizing water with my Steripen. I als” (CC BY 2.0) by ryochiji
Steripen” (CC BY-NC 2.0) by AlphaTangoBravo / Adam Baker
IMG_6762” (CC BY 2.0) by Tim Berger
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About the author /

Diane Vukovic grew up camping and backpacking in upstate New York. Now, she takes her own daughters on wilderness adventures so they can connect with nature and learn resiliency. With dozens of trips under her belt, Diane is an expert in minimalist camping, going lightweight, planning, and keeping her kids entertained without screens.

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