Any time we walk outdoors during the day, we are immersed in solar radiation from our nearest star, the Sun. One particular range of wavelength from this radiation, ultraviolet, is notorious for its ability to cause skin cancer in humans.

This intense energy has been harnessed to create a highly effective form of sterilization known as ultraviolet germicidal irradiation. In recent years, a portable device called a SteriPEN) has been developed to treat individual water bottles.

How It Works

Most versions of the SteriPEN have the ability to treat either 0.5 or 1 liter of water. The premise is simple - immerse the bulb in a water bottle, turn it on, and gently stir the water while the light shines bright and eliminates pathogens. The agitation is necessary to ensure that all microbes suspended in the water approach the UV wand during the treatment.

^{This half-liter soda bottle would not be ideal to use with a UV wand. Image modified from source under Pixabay License}

The device can recognize if the bulb is not fully submersed in water and will indicate if the treatment fails. Note that because of the size of the device, it is generally not possible to effectively treat water in narrow-mouthed water bottles with this method.

Wide Reach

In ideal conditions, ultraviolet light pens have the ability to kill nearly all microscopic organisms including bacteria, viruses, and parasitic protozoans. The radiation causes alterations in the DNA in the cell(s) of the organism, inhibiting the execution of biological functions vitally necessary for survival.

^{A gaggle of E. Coli, one of the many bacteria that can make us sick. Image modified from source under Pixabay License}

The amount of time that is required to safely treat the water depends on the volume of water and the model of the device, but generally at least one minute of treatment is necessary to ensure that potential pathogens in the water are sufficiently exposed to a lethal radiation dose.

Battery Burden

Because this form of water treatment requires a battery, there are extra caveats related to relying on it during a long distance hike. Many models now contain a Lithium-ion battery that requires a USB connection or outlet for recharging. While a full charge may treat several dozens of liters of water, once the battery is drained the device is completely ineffective.

^{Power banks like these are an essential tool for any modern distance hiker. Image modified from source under Pixabay License}

Due to this drawback, a solar charger and battery bank are required for extended backcountry journeys to ensure continued functionality of the device. When contrasting this battery draw with other important technologies like cell phones, headlamps, and emergency GPS beacons, the burden of an additional battery device becomes even greater.

Ultra-Fragile

Another major drawback of this technology is that it is prone to breaking. If the bulb breaks or burns out, or if something goes wrong with the internal circuit board, display screen, or battery, the device is effectively rendered useless.

^{Glass is brittle; bulbs can break. Image modified from source under Pixabay License}

I have personally witnessed the fragility of these, seeing one stop working after it fell a very short distance onto a padded seat cushion (while protected by the included travel case). When relying on something this sensitive, it is always a good idea to bring a backup treatment option in case of failure.

Beware of Silt

A final word of caution regarding these devices is the fact that they require mostly clear water in order to function properly. Cloudy water that is heavily laden with suspended particles like silt and clay will not treat properly, as the particles absorb the light and prevent the UV radiation from penetrating the fluid and neutralizing any existing pathogens.

^{Muddy waters permeate the nightmares of UV wand enthusiasts everywhere. Image modified from source under Pixabay License}

Many flowing water sources encountered in the wilderness will have suspended sediment that prevents the UV light from being effective. If water is collected after setting up camp for the evening, the sediment can be filtered or allowed to settle out so the clear water can be decanted before treatment, but this requires additional time and planning that is not always practical while trekking.

UV Pens in Summary

Effectiveness: Moderate
Expense: High
Effort: Low
Efficiency: High
Durability: Low
Taste: Great

^{A UV wand in action inside of a large-mouth 1-liter plastic water bottle. Image by Coronium, modified from source under CC BY-SA 2.5}

Ultraviolet radiation is a good way to treat water in some situations. Portable UV wands are becoming more affordable, lightweight, compact, and durable, but there are several drawbacks that could prevent these devices from effectively treating water.

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