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SteriPEN vs H2O Amigo: A Long Distance Hiker’s Comparison

Cutting-edge solar-powered UV water purification or simple gravity filter? I took both on the CDT to compare/contrast their performance, durability, and usage.

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by Dan Feldman | 2011-03-08 00:05:00-07


The SteriPEN Adventurer Opti and the H2O Amigo Pro are both innovative and effective means for treating water in the backcountry, but the two products otherwise share little in common.

SteriPEN’s story has been one of overwhelming success and rapid adoption amongst backpackers. After selling its first unit in 1999, Hydro-Photon Inc, the makers of SteriPEN, now offer no fewer than ten versions of the SteriPEN and market not only to the backpacking community, but also to the military, emergency rescue agencies, and the general traveling public.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 1
SteriPEN in solar case.

The success and attention surrounding SteriPEN lies in a breakthrough, and admittedly glitzy concept in water purification: the use of ultraviolet light from a handheld pen-shaped device to scramble the genetic material of water-borne pathogens, making them incapable of reproducing. This technology is a clean alternative to more traditional water treatment methods involving chemicals or filtration. The Adventurer Opti is the ultralight version of the SteriPEN and can be used with disposable or rechargeable CR123 Li-ion batteries. For those not keen on buying disposable batteries or relying on the power grid, SteriPEN makes a solar charging case exclusively for the Adventurer Opti.

The H2O Amigo occupies the more subdued realm of the gravity filter. Far from being on technology’s cutting edge, the gravity filter’s basic but effective design uses a water-holding bag that contains a filter with a small tube at the bottom for water output. The bag is filled, hung, and water moves passively from the bag, through the filter, and out to another bag or a drinking bottle for consumption. It’s essentially pump filtration without all the work of actually pumping.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 2
Amigo full setup.

A quick-drying, lightweight SilNylon bag with durable drawstrings and a single open-ended output hose make the Amigo perhaps the most no-frills, elegantly designed gravity filter to date. Sadly, the Amigo is no longer in production by its manufacturer, Ultralight Adventure Equipment. MSR, Katadyn, Cascade Designs, and Sawyer Products sell their own gravity filters, but none match the lightweight simplicity of the Amigo. Used Amigos can still occasionally be found online, but these tend to be few and far between. More importantly though, the Amigo’s simple design and obtainable raw materials permit at-home construction. This subject has been discussed in great detail on BPL’s own forums.

The aim of this study was to compare the solar-powered SteriPEN Adventurer Opti with the H2O Amigo Pro for use in long distance hiking. Both devices were used alternately along 800 miles of the Montana section of the Continental Divide Trail from July 19 to September 28, 2010 to provide drinking water for a companion and myself. While one device was in use, we shipped the other ahead to a mail drop location. Once at the mail drop, we switched devices, shipping the other ahead to the next mail drop. Practical considerations for long distance hiking for each device were noted. These included observations and recorded data on each device’s weight, cost, performance, maintenance requirements, durability, and ease of lightweight modification. Temperatures ranged from the mid 80s to the mid 20s F. The Amigo was outfitted with a new Katadyn Hiker filter.



A total of 71.5 liters of water were treated with the Amigo and 107.0 liters with the SteriPEN. We primarily sourced from clear bodies of water with good flow. We occasionally got water out of lakes or from cattle contaminated sources, but never needed to pre-filter. Except for the initial charge, which was done using the supplied power adapter, the SteriPEN was charged in the field using the solar charger. Batteries were not removed from the SteriPEN when placed into the bounce box for shipping.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 3
SteriPEN solar case.

Speed and Water Quality

Both devices produced clean tasting water and neither of us became ill. They provided water in a timely fashion with neither exceeding two minutes per liter, unless the SteriPEN’s battery ran out mid-treatment. At the end of the trip, both devices were tested with clean tap water. The Amigo made one liter in 73 seconds and the SteriPEN in 93 seconds. Priming the Amigo’s filter by sucking water through the output hose was necessary in order to start the flow of water.


We appreciated the hands-off nature of the Amigo. Being able to fill the bag and hang the Amigo from a tree branch or rock while we went about other chores or relaxed was a big plus. We did need to be careful to make sure our Platypus was placed carefully under the Amigo’s output hose so that it wouldn’t tip over as it filled. The SteriPEN, requiring constant stirring for about 90 seconds per liter, was obviously more hands-on. This was not too bothersome for small quantities, but when we wanted to make multiple liters, sitting and stirring started to become tedious and, in cold, wet weather, fairly unpleasant.

Since we carried small-mouthed collapsible 2L bottles, we were not able to treat our water directly with SteriPEN, which better accommodates a wide-mouthed receptacle. However, we were able to avoid packing an extra bottle by putting water to be treated in our cook pot, and treating the water there. We did find it somewhat inconvenient to have to dig out our cook pot each time we wanted to treat water.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 4
SteriPEN in pot.

We found that the Amigo was easy to pack and I usually kept it near the top of my Granite Gear Vapor Trail pack. The SteriPEN, while in its charger case, was a little more cumbersome. As we were in Montana and thus often walking in partial or full sun, it made sense to carry the solar charging case outside and on top of my pack. The case was, however, sometimes a challenge to secure. The case’s plastic belt-style clip fit quite loosely onto my pack straps and was therefore not very reliable to use. I eventually settled on lashing the charger down using the two cross straps at the top of the pack, although this was still a loose attachment when my pack was not full.

We did not use the flashlight function on the SteriPEN.


SteriPEN’s published manual advises users to remove batteries from the device when not in use. We learned this lesson the hard way. When putting the SteriPEN away for a few weeks, we failed to remove the batteries from the device. With the second set of batteries just partially charged, we found ourselves constantly changing the batteries back and forth when the device returned to use. The set of batteries that were inside the SteriPEN had mostly discharged, and the charge left in the second battery set was only enough to treat 3-4 liters. Coupled with a few cloudy days on the trail, we never were able to fully charge one set of batteries,and thus had to keep switching back and forth between partially charged batteries. We were not able to fully charge the batteries until we stopped in town for a few very sunny days.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 5
SteriPEN on/off.

We did not have any reliability issues with the Amigo, except once when we left water in the device overnight and temps dropped below freezing. The next morning, we had to wait until the ice in the filter and hose thawed until we could treat water. From then on, we made sure to completely drain and dry (if possible) the Amigo each night.


The advantage to both devices is that they require very little maintenance. Because we used the Amigo in mostly clear water, we never needed to scrub the filter. With greater use, I expect we would have needed to scrub at some point. The SteriPEN required zero maintenance.


Despite both devices having sensitive components, neither broke or malfunctioned. For the SteriPEN, the sensitive component is the bulb, which is encased in glass. If this breaks, the only method of repair is to send the device back to the manufacturer. The SteriPEN took a tumble off my pack on several occasions, but was well-protected inside the solar charging case and no damage was done. The case itself began to show small signs of wear by the end of the trip as some of the inner padding near the latching mechanism began to get caught in the latch. With a few weeks remaining, the belt clip on the back of the case snapped off. This didn’t bother us because we found the clip to not be very useful in the first place.

The sensitive component of the Amigo is the SilNylon bag that holds water for filtering. The SilNylon is thin and thus susceptible to tearing on sharp branches. On a prior trip, I actually made a small hole in the bag this way, but was able to easily repair the bag with SilNet sealer.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 6
Amigo Bag - a closer look.

Weight and Volume: (See Figure 1)

At 3.75 oz on a kitchen scale, the SteriPEN Adventurer Opti with a single set of batteries is significantly lighter than the Amigo, which comes in at 7.75 oz of dry weight. However, the solar charging case, with its necessary second set of batteries, brings the SteriPEN system up to 11.0 oz. This combination is .25 oz heavier than a soaking wet Amigo stored in its SilNylon carrying bag.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 7
Figure 1

  Weight (oz)
SteriPen w/ single pair rechargeable batteries 3.75
Steripen w/ solar case and 2 battery sets 11.00
H2O Amigo, dry 7.75
H2O Amigo, wet 10.00
H2O Amigo, dry w/ bag 8.50
H2O Amigo, wet w/ bag 10.75

The H2O Amigo in its SilNylon bag compresses down to 75 in³ and takes up twice as much pack space as the 37 in³ solar charging case. This was a moot point for us as we carried the SteriPEN in its solar charger outside of my pack.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 8
Amigo wrapped.

Cost (see figure 2)

While the SteriPEN with a solar charger is initially more expensive, the H2O Amigo Pro surpasses it in cost after approximately 2,500 liters of water has been treated. WAt this point the Amigo’s Katadyn filter will need to be replaced for a third time. Taking this into consideration, the SteriPEN becomes an increasingly better value for the amount of water treated. Interestingly, the H2O Amigo eventually even surpasses the cost of using the SteriPEN with disposable batteries.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 9
Figure 2

  0L 1000L 2000L 3000L 4000L 5000L 6000L 7000L 8000L 9000L 10000L
SteriPEN Opti w/ Rech. Batteries $150.00 $150.00 $150.00 $150.00 $150.00 $150.00 $150.00 $150.00 $170.00 $181.88 $181.88
SteriPEN Opti w/ Disp. Batteries $100.00 $135.72 $173.32 $210.92 $248.52 $286.12 $323.72 $361.32 $418.92 $456.52 $494.12
H2O Amigo $50.00 $90.00 $130.00 $170.00 $250.00 $290.00 $330.00 $410.00 $450.00 $490.00 $570.00

Certain performance assumptions were made in these calculations. With the exception of liters water treated per charge for the SteriPEN, field-testing did not provide sufficient volumes of water to test capacities experimentally:

  • The SteriPEN rechargeable batteries die after 300 charges. Source: SteriPEN customer service. Field-testing on the CDT revealed that these batteries, new and fully charged, made 28 liters of water.
  • A pair of CR123 Li-ion disposable batteries are capable of treating 50 liters of water before needing replacement. Source: SteriPEN User’s manual.
  • The SteriPEN’s bulb requires replacement after 8,000 liters of water treated. Source: SteriPEN customer service and user’s manual.
  • The Katadyn filter is capable of treating 750 liters of water before requiring replacement. Frequent treatment of murky water and failure to periodically clean the filter will obviously shorten this lifespan. Source: Katadyn product manual.

Cost Assumptions (not including tax or shipping):

  • Disposable CR123 Li-ion batteries are purchased online in quantities of 50 at a cost of $46.99 ($1.88/pair). Each battery is 3V with 1300mAh capacity.
  • Replacement rechargeable batteries are purchased online in quantities of 2 at a cost of $11.88. Each battery is 3V with 650mAh capacity.
  • Replacement Katadyn filters can be purchased online at a cost of $40.00.
  • The SteriPEN bulb can be replaced by the manufacturer at a cost of $20.00.
  • A used H2O Amigo can be obtained online for $50.00.

Ease of Lightweight Modification

Although we chose not to modify either device on this trip, both devices lend themselves to some modification to drop weight. The Amigo’s output hose can be cut to a shorter length and the small plastic hose clamp removed. The cords that allow the Amigo to be hung can be cut and re-tied. On the SteriPEN solar charger, the clip can be removed. Otherwise, the SteriPEN itself is difficult to modify. The plastic cap that protects the bulb can be omitted, but this leaves the bulb vulnerable.

SteriPEN vs H2O Amigo, a long distance hiker’s comparison - 10
Amigo output hose.

Overall Impressions

We found that by the end of our trip we preferred using the H2O Amigo. This was based on the fact that by its hands-off nature, the Amigo, especially for treating multiple liters of water, was more convenient to use and we encountered fewer problems with reliability. Admittedly, the battery issue was our own fault, but we also value not having to worry about battery charges and changes on backpacking trips.

The added convenience of the Amigo, comes with a significant difference in monetary price. However, the long term savings associated with the SteriPEN currently adds a significant cost in weight, as the solar charger with its second battery adds an extra 7.25 oz, negating the SteriPEN’s weight advantage over the Amigo. With some design changes to the SteriPEN’s solar charging feature, this would be a closer call. Reducing the size of the charging case might be a possibility. Using a lighter material to make the case would be another. This would expectedly increase the cost of the case, but since the cost savings with the solar rechargeable feature is so significant, this might not be a tough sell. Finally, designing the solar charging case to charge the batteries while still inside the SteriPEN would reduce weight by eliminating the need to carry a second set of batteries. It would also add a considerable amount of convenience to the entire system.


"SteriPEN vs H2O Amigo: A Long Distance Hiker’s Comparison," by Dan Feldman. (ISSN 1537-0364)., 2011-03-08 00:05:00-07.


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SteriPEN vs H2O Amigo, a long distance hiker’s comparison
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Dan Feldman
(podin04) - F
General Comments on 03/12/2011 09:59:15 MST Print View

First, thanks to everyone for providing such good discussion around the article. Reading comments is what I enjoy the most about writing. Second, I want to address a few recurring themes in the commentary:

VIRUSES. It is true that the Katadyn filter inside the H2O Amigo does not offer virus protection. It is also true that the incidence of backcountry water-acquired illness due to viruses in the USA is unknown. There is not sufficient scientific data exploring how often viruses make people sick in the backcountry. However, even if there was such data, it would invariably be limited to specific geographic regions. This is because the types and quantities of contaminants in a waterway are dependent on land use patterns. Waterways downstream of population-dense communities are more likely to contain traces of human waste and therefore to contain viruses that make people sick. Waterways near areas with spare human population or are upstream of large communities are less likely to contain viruses.

When discussing backcountry water treatment, various technologies shouldn't be thought of as "better" or "worse" based on the absolute number or type of contaminants filtered, destroyed, or otherwise rendered harmless. Performance metrics aside, a water treatment technology is only as good as where it is planning to be used. For instance, a technology that does not offer coverage for viruses might be a bad choice for thru-hiking the Potomac Heritage Trail, which passes by a large number of densely populated areas and ends in Washington, DC. On the other hand, a technology that covers bacteria and parasites, but not viruses, is perfectly acceptable for hikes in sparsely populated areas.

WHY I CHOSE A DISCONTINUED PRODUCT: An area of interest of mine has always been low tech vs high tech in the backcountry. This article was thus an extension of this curiosity, where the H2O Amigo was the the best representative of the gravity filter concept, even though it has been discontinued (and perhaps making a comeback!?) My assumption was that since we, the readers of BPL, value ingenuity and ease of at-home modification and since the H2O Amigo can be made at home for low cost, this article was relevant.

Dale Wambaugh
(dwambaugh) - MLife

Locale: Pacific Northwest
Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/12/2011 11:08:42 MST Print View

The review covers some interesting points, but I think the technologies are too diverse. An article with an overview and comparisons of electronic purifiers (UV and MIOX), chemical treatments, and filters is needed, with a separate article on each of the categories in detail.

The review is for a discontinued item, but there are a number of available gravity filters in the same class and should have been covered:

Katadyn Base Camp
Platypus GravityWorks
MSR AutoFlow Gravity Microfilter
Aquamira Frontier Pro
Sawyer gravity filters

Since there are dependable components available, a MYOG article on gravity filters would be very interesting.

As to the Steripen, the manufacturer does state that it takes 2-5 days to recharge the batteries with the solar charger. I think that takes it off the table as a viable hiking option with the rechargeable batteries. That option is better for remote/3rd-world use where AC power and battery availability are limited. I do use one and I remove the batteries for storage. I think it makes an excellent day hiking option, where you want to be able to use the water quickly. I back up any of my mechanical water purification choices with MicroPur tablets.

The Steripen and chlorine dioxide options make a good pairing. You can stretch battery life by treating water overnight and using the UV option for quick access during the day.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
H2O Amigo on 03/12/2011 13:14:37 MST Print View

The Amigo is slated to be released, again, better'n ever.

Dan Feldman
(podin04) - F
Re: Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/12/2011 13:33:17 MST Print View


I must respectfully disagree with your implication that the technologies covered in the review are "too diverse" for comparison. A cross-technology comparison of water treatment methods is important because each technology has its own benefits and drawbacks specific to the technology as a whole. Such a comparison allows a user to decide which of these benefits and drawbacks are more suited to his or her own situation (mine was distance hiking in western Montana). From there, the decision about which specific model of technology to use can be made. I think this might be what you are looking for, which was not the aim of this particular article. I am surprised that there are not MORE cross-tech comparisons on gear test sites.

Had I had the time and financial resources, I might have liked to have covered more gravity filters and UV pens and had a really large cross-tech comparison. A significant problem, however would have arisen: As this was real-life field testing, we only drank so much water each day. Including four or five other devices would have meant less water tested per device so, statistically speaking, the comparisons would have been less powerful and some of the issues described in the article (the fraying SteriPen charger padding and broken clip) might not have come to light. So, at my own discretion, I decided to go with what I felt were the best representations of each technology.

There is already a very good gravity filter MYOG article published on this site by Bill Fornshell:

The 2-5 day battery charge requirement DOES NOT take the rechargeable option off the table if the device is carried outside the pack where it can charge throughout the day while the other set of batteries is in use. It does, however, make it a less attractive option along trails that receive limited sunlight.



Matt DeWitt
(tritan) - F

Locale: Midwest
Re: Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/12/2011 13:49:32 MST Print View

Did you make a filter bag for it? Any pics or directions , videos? I am interesting in a gravity filter like the amigo. The Kadyden is 70.00 bucks and group size. I just want a smaller lighter weight version does sawyer have that?

Matt DeWitt
(tritan) - F

Locale: Midwest
Re: Another Sawyer fan on 03/12/2011 14:00:36 MST Print View

do you have a link to the filter you use? Is there a set with water bag or bladder and filter in one?

Craig Price
(skeets) - MLife

Locale: Melbourne, Australia
a plus for steripen on 03/17/2011 23:47:12 MDT Print View

well, despite other's concerns, I'll put in a plus for the steripen. I've used a steripen regularly for 3 years and have never had any issue, and I regularly drown it and beat it about, as it's on my waist belt when I fish and I'm nver one to worry about stuff and have been been kinda rough with it in the process.

I find it is perfect to replace my water in a small gatorade bottle (600ml) which I drink as I fish, quite handy and more superior for this purpose than the filters.

My only niggle is that, of course, steripen can't do anything about the flavour of the water - it's safe, but there've been times when I wished for a carbon filter to "cleanse" the taste on the palate a little, e.g. when I've been fishing areas with livestock near the water (bleh).


James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: a plus for steripen on 03/18/2011 05:20:53 MDT Print View

"... it's safe, but there've been times when I wished for a carbon filter to "cleanse" the taste on the palate a little, e.g. when I've been fishing areas with livestock near the water (bleh)."

Ha, ha... Yeah, I know the problem. Have you tried a few grains of crystal lite? Usually,
a little packet(To-Go or something) will bo two or three bottles.