Ultraviolet Water Purification 101

Ultraviolet Water Purification 101

Ultraviolet Water Purification Systems are a popular choice for backpackers because they’re easy to use, fast, lightweight, and don’t leave any aftertaste in your water like chemical treatments. They are not subject to freezing which destroys most water filters and can be used in below-freezing temperatures to purify cold water. Plus they protect you against viruses because they are purifiers and not filters.  But like all backcountry water treatment solutions, ultraviolet water purification has its PROS and CONS, and is not suitable in all circumstances.

Ultraviolet Water Purification was originally spearheaded by a Maine company called HydroPhoton which made a product called the SteriPEN for hiking and backpacking. HydroPhoton was acquired by the water filter company Katadyn, makers of the BeFree Water Filter and Hiker Water Filters in 2017.

Are Katadyn’s UV Water Purifiers the same as SteriPENs?

Yes. When Katadyn acquired HydroPhoton in 2017, they retired several of the older SteriPen models and have started releasing new products, like the Katadyn Ultralight UV Purifier based on the underlying Ultraviolet Light Purification technology. You may still be able to find some of the older models with the SteriPEN brand name in retailer outlets.

ModelBatteriesLiters Treated / Batteries or ChargeWeight w/ Batteries
Katadyn Classic 3AA (4)Lithium: 1506.3 oz.
Katadyn UltraUSB-onlyFull Charge: 504.9 oz.
Katadyn Opti AdventurerCR123 (2)CR123: 503.8 oz.
Katadyn AquaAAA (4)Alkaline: 50
Rechargeable: 100
6.2 oz
Katadyn Ultralight UVUSB Rechargeable: 20Full Charge: 202.6

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 National 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 an Ultraviolet Water Purifier effective against?

Ultraviolet Water Purification protects you against many microscopic biological contaminants, including:

  • Viruses, including Hepatitis, Norovirus, and Covad-19.
  • Bacteria, including Campylobacter, E. Coli, Salmonella, and Shigella.
  • Protozoa, including Giardia and Cryptosporidium which can cause severe diarrhea. Giardia, often called beaver-fever, is the most common form of 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.
The SteriPEN Adventurer Opti Ultraviolet Water Purifier
The Katadym Adventurer Opti Ultraviolet Water Purifier

What about mineral or chemical contaminants and industrial pollution?

Ultraviolet Water Purifiers do 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 MSR Guardian which is designed (and certified by the EPA) to remove them if they’re a concern.

How do Katadyn’s Ultraviolet Water Purifiers Work?

Katadyns UV Water Purifiers are ultraviolet lights that you immerse in a bottle of water. Rather than removing biological contaminants including viruses, bacteria, and protozoa, they kill their DNA so they can’t reproduce if you ingest them. If they can’t reproduce, they can’t make you sick by overwhelming your digestive or immune system. It’s a subtle but important difference.

What water bottles are Katadyn’s Ultraviolet Water Purifiers compatible with?

Katadyn’s UV Purifiers work with a wide variety of bottles and containers, but be sure to read the directions that come with your unit or contact the company if you have any questions. While they 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 back into the tube, avoiding treatment. When in doubt, your best bet is to use a Katadyn Ultralight Water Purifier with a wide mouth half-liter or one-liter bottle from Nalgene, which is sure to work. You can also use a cooking pot or even a plastic bag as a container.

Does the Katadyn UV Purifier treat 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. Instead, Katadyn 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, you can use a container that does not have bottle threads like a cookpot instead and pour the purified water into a water bottle to avoid the issue entirely.

How much water can you purify with an Ultraviolet Water Purifier?

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

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

Can an Ultralight Water Purifier neutralize tapeworm eggs?

The Katadyn Water Purifiers listed above have not been tested against worms eggs. I would suggest you play it safe and use a filter instead.

Can you only use a Katadyn Ultraviolet Water Purifier to purify clear water?

A UV Water Purifier should only be used to treat clear, non-murky water, without floating sediment. However, Katadyn sells a pre-filter that can be used to clarify water if it is murky.

What about reddish, highly tannic water?

If the water has a high-tannin concentration, Ultraviolet Water Purification will not be effective. 

See Also:

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  1. How does the Camelbak UV purifier compare with the Katadyn?

  2. Philip,

    When you hike here in the NE, do you still prefer to filter or have you switched to UV? Why?


    • I only use UV in early spring or late autumn when a filter would freeze (and be destroyed). Otherwise, I just use a Hydroblu filter. I’d rather not depend on batteries and its faster for filtering a larger amount.

  3. Hi Philip, I’m considering this pen for a throughhike of the JMT. However, reviews seem to be mixed and there appear to be quite a bit of complaints about the device failing after a few uses. What have you heard about this? I would of course also bring another method of filtering or decontamination, but with weight at a premium I am not interested in adding half a pound of unreliable equipment. Thanks.

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