Used it a total of 3 months on the road. Never got sick. Some tips, no particular order:
1. Buy one large silk neckerchief, 2 Nalgene HDPE narrowmouth bottles, 4 high-capacity AA NiMH batteries, and a wall charger. The neckerchief is your filter for "floaty stuff" and the Steripen snaps into the mouth of the Nalgenes like it was made for it, providing a watertight seal. Shake instead of stir, and no spilled water! Buy all this and never have to find bottled water in rural China again!
2. Dry it thoroughly before storing! Otherwise you'll get scale (limestone) buildup between the sensor electrodes and the pen will refuse to start.
3. With NiMH 2500mAh batteries, you can purify about 40 liters before a recharge.
4. Note that the Steripen DOES NOT remove harmful chemicals like oil or gasoline from water! To fill your water bottle safely from a source with oil or other petrochemicals floating on the top, submerge the bottle first under the water mouth down, wipe off the mouth underwater, and turn the bottle right side up to fill. Cap the bottle underwater and bring it back out.

The last reviewer sums up my position on the "Why carry it if you also need to carry a back-up?" It is unreliable at best.

Why do I need to have the proper salinity to have the unit work, why not have an override that will allow me to turn on the light?

Why carry all those heavy extra batteries, why not have a hand crank to charge a Li-on battery?

Filters are tried and true.

I spent four days in the backcountry with the SteriPen and if the proof is in the pudding, then this method of treating water passes with flying colors; no one got sick. There are really two reasons I gravitated toward the SteriPen: 1) size/weight; 2) shelf-life. The first speaks for itself; the SteriPen is lighter and packs smaller than a filter. As for the second, perhaps a little history is in order. It's been about ten years since my last backpacking trip (kids, new jobs, plenty of distractions...). Back then, I had one of the top-rated filters out there, the Pur Scout. When I was planning for my latest trip back into the wild, I wondered about whether my filter would be OK after years and years of storage. So I figured I'd buy a new cartridge, just to be safe. Of course, I came to find out that Pur got out of the hiking filter business, which they appear to have sold to Katadyn. Katadyn sells a filter that seems to fit the Scout, but it's a bit different (no iodine resin?). This all gets me thinking: will a filter purchased today be "serviceable" ten years from now? Designs change all the time. How long will replacement cartridges be available? Given that uncertainty, the SteriPen was attractive. After ten years of storage, there won't be any doubt about the soundness of the SteriPen's functionality (like there would be with a paper or ceramic cartridge filter). Either the light will turn on (and I'll know it works) or it won't. No "well the cartridge seems OK, but it's hard to say..." and then the inability to buy a new cartridge. I like the certainty the SteriPen promises in this regard. So back to the SteriPen itself. I used the pre-filter and the pour-through method. The sequence is a bit tedious, but after a few times, it's no big deal. Short cuts, including the submersion method, would no doubt cut some steps and make things quicker. When it comes to treating water, I'm pretty anal, since the price for sloppiness can be pretty steep. Your threshold might be different than mine. One of my backpacking partners brought his brand new ceramic filter on our trip as well and after one day of filtering, his filter was reduced to a trickle and thus required cleaning. There are two points to make here: 1) there's none of that nonsense with the SteriPen (a good thing); 2) with the SteriPen you don't "filter" the water, so you drink the "minerals" (an indifferent thing, but a difference for sure). My only niggle with the SteriPen has to do with the pre-filter, the threads for which might be a little "soft." Mine got buggered up right away (maybe I overtightened it--which is definitely possible--or cross-threaded it). Not a huge deal--it still works fine--but a little better (over)engineering might make the pre-filter idiot-proof.

I gave the SteriPen a four star rating simply because I have only one backcountry experience with it. In reality, it's probably a five-star product. Don't hesitate to pick one up for your next backcountry excursion.

It may be hard to believe that stirring a UV light in some water will purify it and there really is no signs that it is doing its job but I must say that while i have used this pen i have never had an health issues from drinking water treated with this pen. It is very easy to use, light, compact and doesn't effect the taste of the water. I did however have an issue with it when it refused start. Instructions suggested drying it out and an hour or so in the sun seemed to fix the problem that never returned. You can also buy a filter/steripen bracket that screws into the top of a nalgene bottle that is very handy in water that has 'bits' in it.

While my wife and I used this for 5 weeks while backpacking across the country this past summer, we found the batteries dead at least once. Thankfully we had a backup plan, but it got me thinking: why bother with this, if you're going to carry a backup plan?

Yes, the SteriPen can purify 1L in 90 seconds and we never had any problem that appeared to be related to water, but for something this fundamental reliability is key. With a chemical treatment you know how many doses you have left. With this, you have no idea if you have 100L or 1L left, and who knows, if the button gets hit in your pack or the temps kill the batteries, your new batteries may be dead tomorrow morning.

There are plenty of chemical treatment options that can purify your water very quickly. Many are as light or lighter than this and you know exactly how much you have left.

I like the steri-pen, I really do. But if I'm going to carry a chemical backup plan, why am I carrying this in the first place?

If you're backpacking or camping where you have an infinite supply of water (therefore don't need to carry all your water with you), this is a must have. I used it for a week-long trip in the Boundary Waters along w/ the pre-filter (attaches to Nalgene bottles only - the threads are very specific). No problems the entire week. Brought extra batteries but never needed them.

This device is easy to opperate, effective in treating water, and is light weight. It is great for backcountry use and international travel. The only thing to keep in mind is do you want your water treatment depending on a battery?

I spent a month in Uganda drinking from a mud hole. Given, I needed a Sweetwater to purify the muck out (so that the Steripen could work properly). I give it full credit for me not becoming dead, or worse! ;) Actually I never even got sick. Trust it! It works!

Great concept in a compact unit. Only negative is the small possibility that not all of the water (the amount that remains on the threads or top of the container that you use to obtain the water) will be sterilized. Great alternative to chemicals or the hassle of pumping water. Also AA batteries are easy to obtain around the world which will purify a lot of water.

When the water already *looks* clean, but you know there are *things* living it, reach for the SteriPEN. It's small, easy to use, effective and doesn't change the taste of fresh mountain stream water. (Just make sure you have spare batteries, just in case!)

My wife and I took a year off and travelled through South America(3 months), North Africa(1 month), the Middle East(1month), India(2 months), SE Asia(4 months) and China (1 month) on a tight budget. Our steriPen was probably our best buy overall. We didn't dip any water out of the Ganges or anything, but we never got sick (due to water!) through out. One thing that I think is worth mentioning too, is the fact that you aren't buying bottled water and you aren't throwing away a bunch of plastic bottles. Lastly, we used rechargeable batteries which fit both our camera and the steriPen. (The portable charger was small enough to offset the inconvenience.) In short, not only was it an effective tool, it also is incredibly efficient.

I have the SteriPen classic with the pre-filter and I love it. It's convenient, it's easy, and it's extremely fool proof. All you have to do is literally stick it in water and turn it on. I use NiMH rechargeable batteries and I haven't had a problem yet but I am sure to keep extras with me just in case. The prefilter works for 4 micron particles but you could always use a coffee filter if you had to. However, I must say, I have yet to use my SteriPen in cold weather or at a high elevation so my review may not be as comprehensive. Regardless, all things considered, it is well worth it.

you can spend a good bit less or more on comprable sterilizers, but no need; this is the best bang for your buck! i used it on a 4-day camping trip & had no problem. my girlfriend was the "h2o girl" most of the time and she loved it - "simple to use." we plan on taking it w/ us to nicaragua & costa rica in december. to me, this purchase shouldn't involve much thought; read the reviews and be confident that you are buying a high quality product that will last a long time.

I used this pen up in the Swiss alps on glacial water and didn't have to worry about getting sick the water tasted great....didn't have to worry about chlorine taste in order to kill off bacteria and viruses. I'm pretty sure its probably a bit larger than the newer models but the price was a plus, and I didn't have to spend loads of money to get great results. I'm going to be sure to bring this on every trip of mine...

Just took this to Nepal. Worked great. This is more a note that I certainly didn't see the 125 litre battery life other folks here seem to have gotten (granted I purified a litre at a time, not 16oz). On rechargeable NiMh batteries claiming a 2000mah capacity, I got 31 litres out of the first set of batteries. With the second set I brought, I had unfortunately left them loose in a plastic bag. Unknown to me at the time, as the batteries bang together in the bag (even without completing a circuit), they will slowly discharge each other (I figured this out as I was moving stuff around in the tent and saw small sparks as the batteries contacted each other). A strip of masking tape to keep 'em in line would have saved me some grief. So, I bought a set of duracell titanium alkaline batteries. They finished out the trip at 13 litres with a little gas left, but they had to 'rest' between litres for a couple of hours (the NiMh batteries would do 3 litres back to back no problem). Maybe my NiMh batteries are the problem, maybe it was zapping multiple litres in succession, but I'm not picturing 125 litres out of any set of batteries (even if they're rated 2600mah). Don't take my word for it, though, try 'em out before you go -- give 'em a full charge, and zap a litre morning and night for two or three weeks (or however you expect to use them) to see how long they'll last you. Consider buying a bunch of Propel (or similar) flavoring packets for the water, too, it makes the off taste stuff a lot easier to drink for your wife :)

Months of usage and I can't be happier, this is a really exceptional water filter. The batteries last for freaken ever! Fairly small and light weight especially compared to other water purifiers. This thing couldn't be simpler. Even the most tech deficient people will have no problems. My heeler figured it out. The only down fall is that purifying gallons takes quite a while. Bottom line, how could you not like it?

Used this on my first backpacking trip; I am very glad I did the research and bought this instead of tablets. It fits inside of a 32oz nalgene wide mouth bottle, it is very light, and worked without any issues (I tested it the first night on some fairly dirty water without incident). Pair this with the Steripen pre-filter (sold separately) for a very light weight water purification solution.

This is light and works perfectly. I used it for a two and a half week trip with no replacement batteries required, purifying around six liters each day. I had no problems with any sickness (with I suppose would be the only way to tell if it really works or not). As long as you have a container big enough (at the opening and to submerge the whole light) it is an excellent buy.

I ordered the SteriPen and a few other items. They arrived in a box that was easily 5 times too big, and with no packing material. Granted the SteriPen comes in its own box, and is blister-packed inside that, but it does include a glass bulb, electronics, etc. So, I contacted Backcountry, they agreed it wasn't packed properly. They reminded me that I can return any item anytime for a full refund, and suggested I could wait until a problem developed and then return it. I pointed out that I didn't want to have this thing fail prematurely while on a backpacking trip, so they arranged for me to return this item, and they would send a replacement. Great. Today, the replacement arrived... this time in a box almost 2 times too big. Still no packing material. And this time one corner of the shipping box and one corner of the SteriPen box were crunched. Tired of dealing with this, I went ahead and checked to see if the SteriPen worked. It seems to work. For now. I guess I'll just have to rely on Backcountry's "forever" return policy, and hope it doesn't fail while I'm in the backcountry. Honestly, would it hurt so much to add some crumpled newspaper to your boxes to protect electronics?

I get tired of my right are being so much bigger than my left arm after coming home from backpacking trips. The SteriPEN has totally solved that issue. No more pumping a filter and you preserve the great taste of mountain spring water! You light up my life SteriPEN!