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Backpacking with a SteriPEN Ultraviolet Water Treatment System

Backpacking Steripen Water Treatment

The SteriPEN ultraviolet water treatment system is a popular choice for backpackers and day hikers because it’s easy to use, fast, lightweight, and doesn’t leave any aftertaste in your water like chemical treatments. But like all backcountry water treatment solutions, it has its PROS and CONS, and is not suitable in all circumstances.

Neutralizes biological organismsDoes not work with all bottles or reservoirs
Very fastBattery dependent
Non-mechanical, no pumpingDoes not remove chemical or mineral contaminents
Effective in cold or freezing weatherNot effective with cloudy or murky water
Does not affect tasteDoes not neutralize larger organisms, i.e. worm eggs

What kind of contaminants occur in backcountry water?

Backcountry water can contain two different types of contaminants that can make your ill: biological organisms and mineral or chemical contaminants, including agricultural or industrial runoff. Not all sources or regions suffer from both, so it’s best to do some research about water quality and the need to treat your water before hiking or backpacking in a new area. Contacting the local land manager, like the US Park Service, US Forest Service, or state authority that administers the land is usually a good place to start. Local guiding services and hiking clubs are also useful sources of information.

What kinds of contaminants is the SteriPEN effective against?

The SteriPEN protects you against many microscopic biological contaminants, including:

  • Protozoa, including Giardia and Cryptosporidium which cause severe diarrhea. Giardia, often called beaver-fever, is the most common form non-bacterial diarrhea in North America. There are over 1 million cases of Giardia reported in the United States each year with the highest rate of occurrence in New England and Alaska, according to the CDC.
  • Bacteria, including Campylobacter, E. Coli, Salmonella, and Shigella.
  • Viruses, including Hepatitis.

What about mineral or chemical contaminants and industrial pollution?

The SteriPEN does not neutralize or remove mineral or chemical contamination from agriculture and industry, including herbicides, pesticides, and fertilizers. You will need a water purifier like the General Ecology First Need or MSR Guardian which are designed (and certified by the EPA) to remove them if they’re a concern.

How does a SteriPEN Work?

A SteriPEN is an ultraviolet light that you immerse in a bottle of water that “neutralizes” 99.9% of the viruses, bacteria, and protozoa found in backcountry water sources. A SteriPEN doesn’t actually kill these organisms. Instead it damages their DNA so they can’t reproduce in your gut and overwhelm digestive or immune system. It’s a subtle but important difference.

What water bottles is a SteriPEN compatible with?

SteriPENs work with a wide variety of  variety of bottle and containers, but be sure to read the directions that come with your unit or contact the company if you have any questions. While SteriPENs do work with hydration reservoirs it’s important that you not try to purify more than one liter of water at a time, since most hydration reservoirs are larger than one liter. It’s also important to separate the tube from the reservoir at the time of treatment, otherwise water can flow into the tube, avoiding treatment. When in doubt, your best bet is to use a SteriPEN with a wide mouth half-liter or one liter bottle from Nalgene, which is sure to work.

Does the SteriPEN purify water left on the bottle threads?

When you fill a bottle in a pond or stream, some of the water is bound to adhere to the bottle cap threads, and this water will not be purified by the SteriPEN. Instead, the manufacturer of SteriPEN recommends drying the bottle threads with a towel before drinking. Even then, there’s still a risk that microscopic organisms will remain. Most people have a strong enough immune system that they can resist a small dose of organisms, if any are present. The same can’t be said if you were to ingest a full liter of contaminated water. If you have a compromised immune system or it’s still a matter of concern, use a different water filtering and purification method.

How much water can you purify with a SteriPEN?

The number of liters you can purify varies by model, as shown in the table below. While battery life is good on SteriPENs, it’s worthwhile to carry a backup batteries or a USB recharger in case your unit runs out of power during a trip. For units that require AA batteries, SteriPEN recommends using Lithium batteries because they will not freeze, unlike Alkaline batteries which contain a water based electrolyte solution.

ModelBatteriesLiters Treated / Batteries or ChargeWeight w/ Batteries
Steripen ClassicAA (4)Lithium: 1506.3 oz.
Steripen UltraUSB-onlyFull Charge: 504.9 oz.
Steripen FreedomUSB-onlyFull Charge: 202.6 oz.
Steripen Opti AdventurerCR123 (2)CR123: 503.8 oz.
Steripen QuantumAA (4)Lithium: 1502.9oz

Can a SteriPEN neutralize tape worm eggs?

The company that manufactures SteriPEN has not tested their products for efficacy against worms eggs. I would suggest you play it safe and use a filter instead.

Can you only use a SteriPEN to purify clear water?

A SteriPEN should only be used to treat clear, non-murky water, without floating sediment. SteriPEN sells a pre-filter which can be used to clarify water if it is murky.

What about reddish, highly tannic water?

If the water has a high-tannin concentration, the SteriPEN will not be effective. If you can filter your water to something that can be described as a light iced-tea, or a light lemonade, then you can treat that volume of water twice with the SteriPEN.

Written 2018.

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  1. I don’t have a SteriPEN but I did look at their prefilter you mentioned. For getting the big lumps out, I just use a mini Coleman fuel funnel that has a screen. It’s cheap, light and… I don’t use mine to filter gas!

  2. I had used Steripen for 7 years before changing to the Sawyer Mini. Never ever had an issue or illness from using the pen.

  3. Regardless of your treatment system, I was taught in scouts forty plus years ago to always rinse the threads of your water bottle after treating. Simply tighten the cap, turn the bottle upside down, and very slowly loosen the cap, then shake the upended bottle enough so that the clean water can rinse off the threads of both the bottle and the cap. Then retighten the cap, turn the bottle right side up, and you are good to go. it only takes an ounce or less to rinse the threads of potentially contaminated water.

    • Gerry, that will only work if the water is purified with a chemical like Iodine or Chlorine Dioxide. Diluting microbes doesn’t make them any less biologically active and they will continue to reproduce.

      The easiest way to avoid this entire issue with a STeriPEN is to use a container without threads. A cook pot for instance. Just make sure you stir and measure the amount of water treated precisely.

      • Philip,
        Interesting thought. I just thought that a thorough rinse with sterilized water would be not different than wiping the threads. But I think I will at least do both in the future to reduce my possible exposure. I had giardia last year from drinking untreated water. I only got the symptoms well after my trip was over and I was back home. Knowing what it was, I made a quick trip to my doctor for the antiobiotic which took care of it quickly but it is a mistake I don’t need to make again. “No wisdom gained in the second kick of a mule.”

      • Gerry, your thought is the same as mine. Seems like allowing some of the purified water to rinse off minute amounts of microorganisms on the threads would be pretty equivalent to wiping them off.

      • He got Giardia the last time did that…

  4. Philip with your experience what is your preferred method in winter as apposed to 3 season treatment of water

  5. I believe I will stick with the Sawyer Mini and/or Katadyn Pump/filter system, though I do see it’s advantages.

    Your note about reddish/tannic water definitely applies to the water sources/creeks, etc. in the Dolly Sods area of West Virginia. The water is very reddish/tannic. They don’t call it Red Creek for nothing!!

  6. I could go on and on about my unfortunate Steripen adventures from a few years back. Hopefully they have fixed their problems since then. I found that the batteries did not last nearly as long as promised. They sent me multiple new units. Same problems. My electrical engineer husband determined that the problem was with their testing protocol. They did not test the units to determine battery life the same way someone would actually use them in the field. Eventually, I believe they took that particular unit off the market. They sent me 2 other types as replacements. One had a solar charger that came with it, the other was the rechargeable unit. I found that I only trusted the rechargeable one as a backup on day hikes. I sold all the ones I had left on ebay and went back to my trusty but heavy MSR. Now I use Sawyer.

    • There’s a reason why we always caution people to not trust batteries outdoors. For me, I always bring two ways to filter/purify my water. You never know when one is going to fail, and they do.

      • I use a filter most of the time now but always have some chlorine dioxide tablets in my First Aid kit… just in case.

  7. Phillip,

    In your article you state “The SteriPEN does not neutralize or remove mineral or chemical contamination from agriculture and industry, including herbicides, pesticides, and fertilizers. You will need a water filter-style purifier to remove them if they’re a concern.” I am not convinced a Sawyer type filter (0.1 micron absolute hollow fiber) is effective against organics (pesticides,etc) or dissolved salts. In the water purification business water purity is often measured by total organic carbon (TOC) and conductivity. (No organics, no TOC and no salts, no conductivity) To achieve low levels of TOC and salts the industry uses Reverse Osmosis (RO) and other methods where the contaminates are removed based on molecular size (much much less than 0.1 micron)

  8. Yes, the older Steripen Adventurer can be hard on batteries. The trickle wattage is fairly high on most. When they switched to the optical version rather than metal plates on the sides, this was mostly cleared up. I seem to remember a 50mA draw, but I could be mistaken. Older versions were well over double that (~120mA.) Yes, rechargeable batteries are not strong enough for more than a few uses of the Steripen (SP, SPA Adventurer model.) Mine lasted a full day, but didn’t make sense compared with regular lithium 123’s (I seem to remember the contact at Steripen said 123’s were lithium despite manufacturer (except rechargeables, of course.) I open it up and flop one battery over eliminating ALL current drain or for storage.

    One caveat with the batteries, do NOT change only one battery. This can easily lead to overheating while in use.

    Do not spill DEET on the case, it will melt it.

    Water quality in the ADK’s and most hiking areas is good. Generally, it is only protists, bacteria and viruses I worry about. Even heavily tannic water can be done using a narrow bottle with the top cut off. Permethrin does break down in the presence of UV. Note, that usually minerals are a GOOD thing in water. Lead, mercury, tin, etc can be toxic, though. They differ. I agree with Philip, do your homework first and insure where water sources are.

    I have been using a Steripen for over ten years with ~60 nights per year out. I have never been sick due to water. (I did ingest crypto with AquaMira, though…sick for a month, off and on. My fault, I rushed the treatment down to a half hour…not good on crypto. Never had guardia, about 30% of the population is immune, soo, I think I might be.)

    I agree, ALWAYS have two forms of treatment when you are out. I have seen many filters fail: Sawyers(wrong backflush methode, filter frozen overnight) MSR Sweetwater (cracked filter on one, plugged filter requiring extra force on the handle on another,) and others (>100nm pore size ie straws, safe is <.5nm) fail.

    AquaMira, drops or tabs, is a good back-up. But, sometimes I do a liter or two at night. It just takes a LONG time to work…(~4 hours as I found out.) It is light, but requires carrying an extra liter of water for "cooking" and a separate liter bottle for drinking. DO NOT mix these up. I avoid carrying the extra 2 pounds, normally.

    ~4.5oz is all that is needed for the SPA, including spare batteries for up to three weeks out. There are three methods I usually take: Boiling(coffee/cocoa/tea,) SPA for general trail duties, and AM drops/tabs for overnight. Overnight treatments of a 2Liter platty works well. I usually drink several cups of coffee, oatmeal in the morning. The second liter I use for filling my empty gatoraid bottles for the day. During the day, I use the SPA to refill my bottles. If I had to, I could just boil water for a couple days, but fuel is always at a premium. I could use the AM drops and simply carry the extra two pounds.

  9. I have been in the water purification business for along time and I won’t leave home without it. It gives me the most confidence in the biological safety of the water. Your comments about cloudy water and prefiltering are correct. I carry paper filters. Coffee filters work well. I generally wipe the rim with unscented hand sanitizer and let it evaporate off.
    Filter fibers can break and bypass untreated water. That being said, I carry chlorine dioxide tablets, the Sawyer mini and extra batteries. I will use more than one method if conditions such as pastures and sewer plants upstream warrant it. My compliments on your review and the website as always are excellent

  10. If you use a 1 ounce pre-filter that filters water down to 1/2 micron (I recommend http://www.dudadiesel.com/choose_item.php?id=PTFEP3S ), you don’t need to worry about worm eggs, wolf eggs, nor sediment. These only cost $5 apiece and can be washed and reused — but at the end of a long hike, I dispose them. Been using these for years. They sell a lot of them to backpackers. I recommend you use a wire cutter and cut and pull out the ring at the top of the filter to get the weight down to 1 oz.

    • That 0.5 micron filter looks to be excellent. And the complement to my Steripen, other than dissolved chemicals. It appears that using this to filter all water going into my Nalgene bottle, then hitting it with my Steripen, there willl be no living organisms, including viruses, in that clear filtered water. Is this a reasonable expectation do you think?

      I dismiss all assertions such as “I’ve been using such-and-such water or method, or doing so-and-so for all these years, and I feel just fine.” Proves nothing, as we learned in junior high school. I’m old, and don’t get sick, and want to stay that way.

  11. I am using a Steripen Freedom with combination of Sawyer Mini as (pre)filter. In many cases this is an overkill. But I never had trouble with water.

  12. I have a Steripen Classic 3, got it a year ago from REI. The worm egg question was discussed before that. They’ve had plenty of time to test it since, so I’m suspicious of why they haven’t given an answer. A clear yes or no or sometimes. Seems like any high school kid could do it as a science fair project with minimal equipment in the biology lab, no? I’m beginning to remember the saying “No answer after a while is an answer.” I may go back to my backup, Aqua Mira or boiling.

  13. James, I agree with the first part. I believe that they don’t test it because they know the results would show them to be ineffective. This doesn’t bother me because I understand why such tests would fail. A 99.999% effectiveness against tape worm eggs is not acceptable. A single egg could infect you, badly.
    Not give you the craps for a few weeks.Other diseases require massive contamination to penetrate your bodies single most potent defense, your digestive system.

  14. I have used the “pen” for over 5 years and just took it on the JMT 23 day hike. I sent myself batteries in each resupply pack becos that IS the one downer for this unit in my opinion. I also carried iodine pills in the event of a problem but it has always worked fabulously and I have no complaints. I recommend it highly :)

  15. When I bought my Steripen I switched to using only lightweight stainless steel water bottles on the theory that the UV light would reflect around inside numerous times, thereby increasing the kill capability, instead of passing through the bottle walls as with most plastic bottles. My next water bottle may be Titanium.

  16. We the advent of so many of our lakes rivers an just water being polluted an the EPA being almost totally useless under the last administration kept busy power grabbing which allowed so many bad things to happen that the public was not made aware of I will continue to use my First Need Deluxe Water Purifier….

  17. I carry one of these (the old Adventurer model) on my business trips to Asia. It lives in my travel rucksack. I occasionally get some funny looks when I dunk it in my water glass at the restaurant, but it’s better than the risk of Delhi Belly. No trouble at all with battery life – I get 30-40 full cycles per pair of 123’s. Good enough for me.

  18. Will these work with smart water bottles or do we have to use wide mouth nalgenes?

  19. Has anyone noticed battery performance issues in cold (below freezing) temperatures?

    • Rick, yes. As with all battery operated devices, you need to keep the temps well above freezing for good output. The bulb itself will get a bit sluggish in below freezing weather, too. It will glow, but not at full strength. After 4-5 seconds it comes up to spec. Keep it in a warm pocket for best performance. Anyway, the current draw for cold objects is always a bit higher than for warmer objects. Think of your fluorescent lights in your garage. They glow kind of orange when the get down to about 20F. Then they eventually kick on. The filament actually is a better conductor when it is cold so it draws more current. After a few seconds they kick on. The glow is actually warming up the bulb a bit before operation. Same for the Steripen. There are some new UV-C band LED’s out there. These work with far less current and last longer. Right now they are expensive, though. I am hoping they come down in price before my Steripen burns out.

  20. Very nice article but one section is IMO very misleading: “The SteriPEN does not neutralize or remove mineral or chemical contamination from agriculture and industry, including herbicides, pesticides, and fertilizers. You will need a water purifier like the General Ecology First Need or MSR Guardian which are designed (and certified by the EPA) to remove them if they’re a concern.”

    The manufacturers of the Guardian and the First Need respectively both claim to meet EPA standards for purifying water of micro-biological organisms. ASFAIK they make no claims about removing dissolved or volatile organic compounds such as herbicides, pesticides, etc. In combination with a carbon filter, some VOCs might be removed but if the water is really tainted with chemicals you would need a lot of carbon.

  21. I feel like I’m out of the mainstream on this subject, but I have a different philosophy about water treatment. I hike in the White Mtns and Maine and I don’t treat my water. No filter, no Steripen, Sawyer filters are too much bother. I look for springs or running water, but if they aren’t there, drink anything available. There isn’t anything in this area that would do anything worse than give you a few bad days or a week, maybe. I was influenced by Yvon Chouinard in various articles I read over the years. Here’s one: https://www.outsideonline.com/1909941/king-dirtbags
    I think I may be immune to giardia, on a recent trip into the Pemi Wilderness I naturally drank all my water from the East Branch of the Pemi. I guess it gave my hiking friend the idea that she could do this too, at least at one water bottle refill and she came down with Giardia. I didn’t. That doesn’t mean conclusively that the Pemi has Giardia, but it could. I have read recently that after a case or two of Giardia, many people become pretty much immune to it. Why not try it for yourself? (LOL) I do make an exception, since I am leaving on a trip to Easter Island in about a month, I now take Aquamira and treat suspicious water with it like at Unknown Pond last week. I have used Aquamira in Nepal where I fill my water bottles out of any faucet I encounter and treat with Aquamira. No clutter of empty plastic bottles, no procuring and buying water and who knows how pure the Bottled water is anyway in Nepal? I had no problems. My only beef with Aquamira is that sometimes those little bottles leak as happened a year ago when I went to use it and the bottles were empty. Left a nice big stain on my otherwise fashionable Osprey Backpack. I have told some friends about my Yvon Chouinard influence and they gave me my trail name which is now “Yvon.”

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