Does the SteriPEN (UV water purification system) really work?

My SteriPen experiments have moved to my new experiments website. Please read them here.

The SteriPen is a UV water purification system designed for hikers, outdoorsmen, or travelers to foreign countries who can't carry enough clean water with them on their adventures. The person is supposed to be able to scoop up some lake or stream water into their water bottles and use the SteriPEN to kill the microorganisms in it before drinking. The SteriPen is very easy to use. It has one button. You press the button and stick the end of the SteriPen into the water and mix it around. There is a visible light ON while the pen is ON. You continue to keep the SteriPen in the water and gently stir while the light is on. Once the light goes off, you remove the SteriPEN from the water and it is done. Many of my website viewers wanted to know how trustworthy this product is. The company has several different SteriPENS, and they kindly donated a SteriPEN Emergency  to me to test. 

About the Scientist

If you are new to my website, let me tell you a little about myself. My name is Annie Pryor. I have a Ph.D. in biochemistry from The Ohio State University. After a few years working in a research lab, I "retired" to be a stay-at-home mom. When my first baby got a terrible stomach virus that required a trip to the ER, I decided to research the subject and created this website dedicated to reducing the prevalence of the stomach "flu" in the world. My 3 little kids keep me busy, but I still get a hankering to do experiments now and then. I've tested cleaning productshand sanitizersproduce washing techniques, essential oilsNorwex ClothsSteriPenslaundrylunch box coldnessthe Phone Soap, spongesand even sunlight. I also happen to be the inventor of a really useful drying rack. I invented it because I needed a convenient place next to the kitchen sink to hang baby bibs up to dry between meals. It is also perfect for drying sports water bottles, dish cloths, food-storage bags, cleaning cloths and many other items. I have a shorter drying rack (12.5 inches tall) and a taller 15 inch rack. The Mommy Genius®  Drying Racks are manufactured in the USA and are available on Amazon. If you would like to be informed when new experimental results are posted, please like my Facebook page

I am also very proud of my daughter, Katie Scarlett. At age 8, she has written, illustrated, and published the first 3 books in a delightful series! Princess Katie and the Fairy Tea Party , Princess Katie and the Mermaid Lagoon and Princess Katie and the Kitty Club are available on amazon. The stories are so sweet and teach about kindness, forgiveness, including others, and doing the right thing. I think every little girl would love them! Please consider buying them for a little girl that you love. Katie gets about a $2 royalty from amazon for each book sold that is getting deposited into her college savings account. 


To test the SteriPEN, my little Michael and I walked to our neighborhood lake to get a water sample. 

I dipped my .5 Liter water bottle into the lake and filled it up. I was careful not to get mud and debris.

When we got home, I used a sterile swab to take a sample of the untreated lake water. 

I rubbed that swab all over an agar plate. I incubated that agar plate in my warm incubator for 24 hours. 

Next, I used the SteriPEN. To use the SteriPEN Emergency , you press the button one time if you are treating 1 Liter of water or 2 times if you are treating .5 liters of water. I pressed the button 2 times because I had .5 liters of water. Then I stuck the SteriPEN into the water and mix it around. There is a visible light ON while the SteriPEN is working. I kept mixing until the light turned off and then took the SteriPEN out of the water. UV light is harmful to people. I wore my UV-blocking sun glasses while I was using the SteriPEN. The SteriPEN is great, though, because it won't turn on unless it is IN water. So, your kids won't be running around with it pretending that it is a light saber. 

I used a sterile swab to take a sample of this UV treated water.

I rubbed the swab all over another agar plate and let that plate incubate for 24 hours. 

Then I treated that same water one more time. I pressed the button 2 more times and stirred while the light was on. 

Then I used another sterile swab, took another sample of the treated water, and rubbed it all over an agar plate. The plate was incubated for 24 hours. 

Here is a picture of this lake water in a clear glass. As you can see, the lake water that I used in these experiments looked pretty clear. 


Here are the results. My negative control (clean tap water) did not have any colonies of bacteria growing. (There is a tiny white dot in the picture on this clean tap water plate but that was a bubble in the agar.) Much too my surprise, the dirty lake water did not have that much bacteria growing in it to start with. Perhaps that is because it is March and the water is so cold. I will try this again in the summer when there might be more bacteria in the lake water. After using the SteriPen for 2 treatments, there was no bacteria at all growing on the plate. 

I repeated this experiment with lake water another day and got similar results. 

Next I decided to make my own dirty water to test. For other experiments that I was doing, I had made "germ water". This is made by taking a small scoop of mud from the back yard and mixing it with purified water. Then I pour it through paper towel to filter out any chunks. I also scraped bacteria off an agar plate from an earlier experiment and mixed that in. So, this "germ juice" had LOTS of bacteria in it. I put 1mL of "germ juice" into .5 liters of pure tap water. 

The water still looked pretty clear after the "germ juice" was added. 

I repeated the same experiment using the SteriPEN once and then a second time. Here are the results. As you can see, the dirty water is MUCH germier than the real lake water from the previous experiment. 2 treatments with the SteriPen killed most of the bacteria. 

I repeated this experiment again using even DIRTIER water that I made. It was really looking cloudy. 

The results show that 2 treatments with the SteriPEN was more effective than one treatment and killed the majority of the bacteria. 


I am impressed by how well the SteriPEN worked. I think it is a very useful tool, and I will keep it on hand for emergencies. It would be great to keep in your emergency kit or to take with you on a trip to a foreign country where the water isn't safe to drink. I cannot guarantee that it will kill every microorganism in your water. There are many types of bacteria that won't grow on an agar plate. There are parasites and other microorganisms that won't grow on the agar plates that I use. So, even when a plate looks like nothing grew on it, I can't guarantee that NOTHING was alive in that water. UV light SHOULD kill these microorganisms, though. Also, according to the SteriPEN directions, it will not kill germs in water droplets that are on the side of your water bottle or in the mouth piece. So, you need to wipe those droplets off before you drink. In addition, they also sell pre-filters to use BEFORE using the SteriPEN. The pre-filters will remove debris and particles of mud that would interfere with the UV light working. In conclusion, I think it is safe to use the SteriPen on outdoor water that LOOKS clear, but I would use it twice. 

Future Work

 I have many more experiments to do!  If you would like to suggest a product or experiment, please e-mail me If you would like to be informed when new results are posted, please like my facebook page. I always post on there when new results are up. If you would like to help support my work, please use my Amazon links when you shop on amazon. I have an Amazon affiliate account. If you use any of my Amazon links when you shop on Amazon, I get a small percentage of the sale. For example, you can click to Amazon using the link for my daughter's book and buy something. It doesn't matter what you buy, but I will get a small percentage of the sale. I use that Amazon money to buy agar plates and all the supplies that I need to do these experiments. If you don't want to bother using amazon links, you are welcome to send me a small donation through paypal. If you really want to brighten my day, please buy one of my daughter's books. They are excellent! If you don't have a little girl to give them to, buy a copy for your local elementary school library or children's hospital. 

If you want to read more of my experiments, please check out this list. 

Lastly, before you leave, please brush up on your knowledge of stomach bugs so you can help decrease their spread by reading this page of my website. Thank you!

--Annie Pryor, Ph.D 
phd.annie at