We tested several types of water. We had water collected from a local pond which houses ducks and geese, we had water we added E.Coli to, and with both of these, we also tested how well the Steri-Pen worked when we added extra dirt to the water. We followed the manufacturer's instructions in using the Steri-Pen. The pen is designed to only be on in the water, and it goes off when it is done. After the UV light goes off, a small indicator light on the pen flashes either green or red. Green means the water is sterile, while red means you need to purify the water again. We spread 140 micro-liters of water on each plate (we used LB media) and grew the plates over night at 37 degrees Celsius (approximately body temperature).
We collected pond water and plated 140 micro liters of it before purifying to use as a control. We then measured out 16oz (the volume of water the manufacturer recommends sterilizing), purified it, and plated 140 micro liters. We then poured another 32oz of non-purified pond water into a widemouth nalgene bottle and purified that and plated 140 microliters. During purification, the UV light stayed on for 50 seconds (with both samples) and the indicator light showed a green light.
This is the pond water. Though the picture does not show it very well, this water is pretty murky and certainly not clear.
The Steri-Pen in action
The plate on the left is what grows from the non-purified pond water. The plate on the right is from 16oz of purified pond water. There is one colony growing on the 16oz plate, and we're willing to bet that whatever grew that colony wouldn't cause any major problems if you drank it (a little science background--each colony comes from ONE bacteria, and chances are one bacteria would rapidly die in your stomach).
Again, the non-purified water is plated on the left. On the right, we plated purified water from the 32oz nalgene. There are no colonies on this plate.
For our "ridiculously high amount of bacteria experiment", we used a strain of E.Coli called DH5-alpha. This bacteria grows readily on LB. We first plated 160 microliters of E.Coli by itself so our readers at home can see just how well this little bug grows. Then, we added 260microliters (about one and a half times what we plated) to 16oz of tap water. We plated that, then purified it and plated it again. The UV light on the Steri-Pen stayed on for 50 seconds and the indicator light flashed green.
The plate on the left is the E.Coli by itself. The plate on the right is from the 16oz of purified E.Coli laced water (there are no colonies).
The plate on the left is the water mixed with E.Coli before purification. Again, on the right is the 16oz purified E.Coli laced water.
Well, we screwed up. We made water so dirty, you'd have to be trying to purify mud. Here's what it looked like:
Guess we got a little overzealous. Oh well, we tried to purify it anyway. In all samples, the Steri-Pen only stayed on for 45 seconds, which shocked us, but we were given a green light (also shocking, we expected red), so we went ahead and plated the purified water:
On the left, we have the water (we used the non-purified pond water again) mixed with dirt and not purified. On the right, this same mixture purified. As you can see, there is a lawn of bacteria on both plates--the Steri-Pen didn't work at all.
Just for comparison sake, on the left you have pond water mixed with dirt then purified, on the right you have pond water purified. Clearly, the dirt hindered the effectiveness.
We also mixed dirt with water laced with E. Coli and purified that. On the left is water plus E.Coli plus dirt, and on the right is this mixture purified. There is no appreciable difference.
Personally, we trust the Steri-Pen. (Though, just a word of consumer warning--REI.com sent us a used Steri-Pen that had a broken latch on the battery case, so we will be exchanging ours for a new one). We plan on more experiments this week with less dirt so that we can see just how cloudy the water can be and still be effectively purified. We were a bit concerned that we were given a green light when the Steri-Pen obviously didn't work, but we justify this drawback by using common sense. There's no way either of us would have drank water that dirty anyway.
We have not had a chance to fully test how long the batteries last, though according to the instruction booklet, my nickel-metal hydride rechargeable batteries should do about 45-50 uses. The UV bulb lasts for 625 gallons of water before needing to be replaced. The device has a warning feature to tell you when either the batteries or the bulb need to be changed.
Since there are no filters to replace, we feel the $200 steri-pen is a good investment. We already have rechargeable batteries and solar recharger, so we'll have no added cost for a long while. In addition, the steri-pen with batteries only weighs about 7 oz. It also comes with a 1.5 oz nylon carrying case (which we recommend carrying to help protect the Steri-Pen).
Be aware that we did not test specifically for giardia, cryptospordia, or viruses. We tested only for bacteria. However, UV light does kill these things and we feel it's safe to assume that if the bacteria was killed, these things were too. And as always, have a back-up. Water is your most valuable resource in the backcountry, so be sure you can use it. We carry iodine as a backup chemical treatment system.
We ran across a nice, mucky looking puddle Monday while we were leaving work. We collected the water, took a picture, plated it, purified it, and then plated that. This result concerns us a bit, but we've decided we will use our iodine if we have really dirty sources like this.
The water (still quite murky, obviously)
On the left is the non-purified water, on the right is the purified water. As you can see, they are both a lawn of colonies (these plates smelled horribly too--they were obviously growing lots of things).