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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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Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: Me too on 03/09/2011 12:38:09 MST Print View

"I SERIOUSLY doubt if the Amigo gravity filter will take out viruses. The SteriPen absolutely will. Thus the SteriPEn is a water PURIFER, and the Amigo is not. The FDA would not classify the Amigo as a purifier."

That's accurate. Katadyn rates the Hiker/Hiker Pro cartridge at 0.3 µm, much too large for filtering viruses (and which they do not claim).



Chris W
(simplespirit) - MLife

Locale: .
Re: Re: Me too on 03/09/2011 12:40:17 MST Print View

In regards to viruses, IIRC they don't exist in US water. Something to note for use in other countries though.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Me too on 03/09/2011 13:25:31 MST Print View

Hi Chris

You do NOT remember correctly ! ! ! ! ! ! ! ! !

Viruses exist everywhere around the world. What do you think causes the common cold? Water in the USA is as suspect as water in most any Western country. Granted, some third-world countries are worse.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Steripen on 03/09/2011 13:31:10 MST Print View

Hi Ken, and everyone

> Buy the batteries online. Cheap.

Buying on line is OK provided that you buy 'brand name' batteries. The Duracell and Panasonic batteries on that web site should be OK provided that they are not 5 years old and not fakes. The other cheaper brands ... are probably not able to provide the 1 Amp needed.

You get what you pay for.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Super Delios is the best system I've found on 03/09/2011 13:35:48 MST Print View

Hi Robin

That is a UK web site, not subject to USA EPA regulation. The Super Delios system only filters to 0.2 microns. It is not a 'purifier' in the EPA meaning of the word, as it cannot stop viruses.

On the other hand, if you want to use it as a filter and handle virus problems separately - it could be fine.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/09/2011 13:38:00 MST Print View

Hi Tony

I have some Sawyer filters here about to go into test.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Reliability on 03/09/2011 13:41:11 MST Print View

Hi Beat

> some water seems not to have enough electrolyte content to be registered by the Steripen
Known, albeit rare, problem for the Adventurer. That's why the Adventurer Opti is a better choice.

> It would occasionally just not light up at all, and often light up briefly, to be followed
> by an error (red light
> increasingly difficult to turn on (it would turn on and immediately turn off),
That sounds like an inadequate battery to me. Happens all the time with cheaper batteries. What brand were you using?


jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: mUV vs SteriPen on 03/09/2011 14:15:54 MST Print View

That looks like a really nice product

Cool packaging - clear case so you can see circuit board inside

Skimpy info on their web site

It says 12 treatments per charge - how many pints is one treatment? How long does it take to treat a pint

Then you can charge the internal battery from any battery with magnetic clips - cool

Is the On/off switch easy to turn on and off? My Adventurer is a real pain, especially when it gets cold.

They said it costs $49 but isn't currently available, check back in June 2010 for availability. Maybe they meant 2011?

They said this is their first product

This sounds like a new company so one might expect some complications ordering and receiving a product

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/09/2011 15:19:31 MST Print View


Great news to hear that you will be running test on the Sawyer filters.

Looking forward to seeing some real scientific testing on them.

Any idea of when that article might be out?


Mads Nielsen
(mpvet) - F
The science on 03/09/2011 15:24:40 MST Print View

Granted I'm not an expert, but I am a vet and have had some dealings with inland fish farming where water purification is a key part of the business. They use UV for purification but only AFTER serious filtration because UV does not work if the water contains particles that can provide shade for bacteria and virus (remember they are quit small). So from my knowledge there is no way that a device like stirpin can work in a trail situation. Do any of you guys have any explanation that would tell me how the system can work?

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: The science on 03/09/2011 15:31:05 MST Print View

You're supposed to stir it and it requires more than a minute to treat

In that time, you'll be exposing all side of any particles

Chris W
(simplespirit) - MLife

Locale: .
Re: Re: Re: Re: Me too on 03/09/2011 15:33:49 MST Print View

I'm not sure where you get your info Roger, but everything I've read indicates the chances of getting a virus from US water sources is basically nil. Of course they exist, water borne or otherwise, but that doesn't mean we need to be paranoid about treating for them.

Mads Nielsen
(mpvet) - F
Re: Re: The science on 03/09/2011 15:38:32 MST Print View

Suppose it depends on standards and the goal is perhaps just to get under the infective dose of a pathogen, but in muddy water I doubt that it's possible with UV light. Furthermore particles are 3D and can hide microorganisms quit well.

Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: The science on 03/09/2011 16:31:08 MST Print View

Hi Mads,

One's supposed to pre-filter or settle turbid water before treatment. The Steripen literature has a maximum NTU value to stay within for it to be effective, as well as physical descriptions of what water looks like at that turbidity (since nobody carries a meter with them). Offhand I don't recall the value.

Also, double-treatment is recommended for poor water conditions. Luckily, a good proportion of high-country water is quite clear. Obviously that's not the case everywhere!



Edited by halfturbo on 03/09/2011 16:31:47 MST.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
re on 03/09/2011 16:58:37 MST Print View

If you use your bulk water container to store untreated water

Let it settle to get clearer water to treat

For water you're going to boil anyway for cooking, no need to treat it, if you just bring it to boil it will kill the bugs according to some link on a recent thread

Then you can save your batteries too

dale stuart
(onetwolaugh) - M

Locale: Pacific NW
Amigo on 03/09/2011 18:03:31 MST Print View

I also have the ULA Amigo.

I was less than impressed with it. I had it fail and had to get a new filter on my 3rd outing. I tried to filter the brown (tannin filled) water that is available on coastal hikes in Washington. But everyone else’s pump style filters also got clogged so I was not too dismayed. Then while hiking the Loowit trail (Mt. ST. Helens), it clogged again do to silt in water. The replacement filters were somewhat pricey back then and then the foam pre-filter in the silnylon came loose, so it has been retired.

I have since gone with Aqua Mira liquid. It is not as thorough as the filters (unless you wait 4hrs) but very convenient. I carry two sports bottles and let one "cook" with the chems as I hike using the other.


Keith Selbo
(herman666) - F - M

Locale: Northern Virginia
No comparison on 03/09/2011 20:29:35 MST Print View

I have a Steripen Adventurer. I took it on one 3 day hike. It worked fine as far as I can tell, but why anyone would want to sit around stirring for 90 seconds if they had a choice is beyond me. I went right back to my Sawyer and Charcoal filter combination. Two drops of chlorine per liter to kill viruses, Sawyer removes cellular organisms, charcoal removes chlorine and many contaminants. I connect the output of the filter directly to my hydration bladder so I don't have to worry about spilling. The best part is hang and forget. I snooze or snack or check my map while my filter does the work.

By the way, all the filters I've owned say freezing compromises them. You should check your instructions to see if the Amigo filter is safe after freezing. I always wrap my filter and water in my pack liner and sleep with them when freezing temperatures are expected. My filter never freezes and I always have water in the morning.

dallas shewmaker

Locale: Southwest
Another Sawyer fan on 03/09/2011 22:16:59 MST Print View

I use the Sawyer inline filter tied into my standard bladder drink tube. Just dip the bladder, put it back in my side pack pocket, and go. It's showing on my shoulder strap in the profile pic. No clean/dirty bladder setup; just the dirty one. My water stops are quick; sometimes reloaded and out before the mosquitos find me. I do have to draw maybe 20% harder on the bite valve than when the filter is not present, but that is about the only downside I've found. Weighs about 2 ounces; nothing to replace; micron protection is same or better than most pump filters; one-time purchase at about $56. I convert a lot of backpackers with it at my store based on my experiences and praise of it; hope BPL's future review concurs.

Edited by dallasshewmaker on 03/09/2011 22:19:01 MST.

Bart Godefroid
lab test of water on 03/10/2011 02:17:24 MST Print View

Interesting article!
However I do miss some lab tests of the treated water. Now you can not know if the filters are actually effective because:
a. the collected water could simply be not contaminated
b. the persons drinking the water could have built a resistance against the contaminants in the water

John S.
(jshann) - F
Re: SteriPEN vs H2O Amigo, a long distance hiker’s comparison on 03/10/2011 02:26:58 MST Print View


Edited by jshann on 03/10/2011 02:30:12 MST.