I was initially skeptical when one of the others brought the pen along, and I was prepared to chemically treat (with chlorine dioxide) all our water. Of course UV is a well-established technology for purification at the industrial scale (plenty of science there) but I was worried about how that could be scaled down, made portable and usable in the field. I worried about user error, and a lot about the Murpheys of power consumption and breakage.

We brought two sets of the recommended lithium batteries, each of which the manufacturer suggests should give 100 treatments. While expensive, lithium has more power, weighs less and has a longer shelf-life. We did not count treatments, but we only used the first set in spite of frequent use.

We used it often for a couple reasons: it’s much faster than chemicals (which take at least 30 minutes, and sometimes several hours to work) and it left no objectionable taste (which, after a few days, can be a big deal). On a lower level, it is also really cool to watch, particularly if you have colored Nalgenes and treat your water at night.

The operation wasn’t bad, occasionally overly-aggressive stirring left the sensor out of the water, which automatically turns off the lamp and requires you to start from scratch. A gentle swirl works better. We found the pen occasionally finicky about a wet sensor or pressing the button too many times, but these were minor, and decreased as we grew familiar with the system. We kept a clean (not sterile) cloth in a zip-lock bag to dry the sensor as required, and to dry the whole thing when we were done (as recommended). The wet cloth was no doubt a home for bacterial, but we reasoned that any that might transfer to the lamp were certainly the first to die. So while it is not very complicated, practice and patience help. I will add here that, as in many things, it pays to read the directions and follow them: this is your health after all.

In terms of trust, I agree with Lordhamster, and while the manufacturer cites a large number of studies “proving” the effectiveness, that isn’t really enough to eliminate all doubt. On the other hand, the leap of faith that this goofy blue light is cleaning the water isn’t much different than the belief an odd chemical smell means “safe water.” All I can really say is: none of us got sick. That doesn’t prove anything of course, but I was happy about it at the time. Still am.

There were a few conditions of our experience that bear mentioning: We were able to get our water out of wells and livestock tanks, so it was **probably** pretty safe to begin with. Our wild water was always clear. Since the UV can’t work in high turbidity water we had coffee filters for sediment, however we never needed them. Above all, we could nearly always draw water from a spigot, so it went straight into the bottle without contacting the threads. When we had to dip and dunk, this system got be a lot trickier, as the UV light cannot treat water droplets on the thread, neck, lid etc. Typically we would designate one bottle for scooping, pour really carefully into the others for UV treatment, and then dose the scoop bottle with a ton of chemicals. Done assembly-line style this worked ok.

So a good investment? you really need to consider your use: for one or two people on a short backpacking trip, chemicals will probably be lighter and simpler. For a large group, however, the weight may start to balance out, particularly if you will not be able to “top off” regularly, so you’ll be low on water and thirsty when you arrive at each source. For international travel, I think the pen comes into it’s own: purifying (not filtering) low-turbidity water available from a tap or spigot for that added reassurance, and fast.

My recommendation, for whatever it is worth, is that I bought one for myself based on my experience. I chose the classic for the ease of battery replacement, even though it is larger and heavier than the “travel-specific” one. When not on a camping trip or international journey, it lives in our “disaster kit” to bolster our emergency water supply in case municipal treatment is in doubt.