In the sixth part of our series on backcountry water treatment, we explore ultraviolet (UV) disinfection. This method uses UV light to reduce pathogens in drinking water. While it may sound like science fiction, UV disinfection is a practical option for the backcountry, with specific guidelines and considerations to ensure its effectiveness.
Introduction to UV Disinfection
UV disinfection involves using ultraviolet light to inactivate pathogens in water. The Wilderness Medical Society formally considered UV disinfection as a treatment method for remote settings in 2019. UV light comes in various wavelengths, and while all UV light is invisible, it is categorized into bands. UVA and UVB are associated with sunburns, while UVC is the germicidal band, effective for inactivating pathogens.
How UV Disinfection Works
UV light in the range of 200 to 280 nanometers (UVC) disrupts the DNA of microorganisms, preventing them from reproducing and making you sick. Unlike filters that remove microbes or chemicals that kill them, UV disinfection leaves the microbes in the water, but they are no longer harmful.
Effectiveness Against Pathogens
UV disinfection can inactivate all three types of waterborne pathogens: cysts, bacteria, and viruses. However, its effectiveness varies, with cysts being the most resistant, followed by bacteria, and viruses being the least resistant.
Considerations for UV Disinfection
Water Condition
Turbidity, or cloudiness, can block UV light and reduce its effectiveness. Water with turbidity levels above five NTUs (nephelometric turbidity units) requires pre-filtration. Dissolved organic matter can also absorb UV radiation or shield microbes, lowering the effectiveness of UV disinfection.
Procedure and Equipment
Using UV light effectively involves following the correct procedure, including proper agitation and using appropriate bottles. UV disinfection does not improve taste, odor, or clarity of water and does not remove chemicals, heavy metals, or other impurities.
Safety Issues
Handling UV devices safely is crucial. Exposure to UVC light can be harmful, and broken UV lamps pose a risk of mercury exposure. Always have backup treatment methods, as electronic devices can fail.
Practical Applications and Examples
Steripen Ultra
The Steripen Ultra (Amazon $170) is a popular UV disinfection device. It features an advanced user interface and an OLED display but has some reliability issues, particularly with battery life and electronic glitches. It uses a rechargeable lithium-ion battery, providing approximately 50 treatments per charge, but actual performance may vary, especially in colder weather.
Steripen Adventurer is another model with similar capabilities at the $100 dollar price point.
Battery Life and Bulb Maintenance
The Steripen Ultra’s UV bulb is rated for 8,000 activations. The lifetime of the battery is about 300 to 500 charge cycles, matching the bulb’s service life. Keeping the bulb clean and handling it carefully is essential to maintaining its effectiveness.
Mercury Exposure
If a UV lamp breaks during water treatment, it can release mercury into the water. The EPA sets a maximum contaminant level for mercury at 0.002 milligrams per liter. Always discard water treated with a broken UV lamp, wash your hands and the container, and use a backup treatment method.
Pathogen Reduction Performance
UV disinfection can significantly reduce pathogens when used correctly. Studies have shown varying levels of inactivation for different pathogens. For example, the Steripen Ultra achieved log reductions ranging from 2.96 to 3.44 for MS2 coliphage, a virus used as a proxy for human pathogens.
Compensation for Inadequate Reductions
To ensure effective disinfection, you can increase the UV exposure time or repeat the treatment. Multiple cycles can achieve higher log reductions, even in murky water.
Conclusion
UV disinfection is a viable method for treating backcountry water, offering significant pathogen reduction when used properly. However, it requires careful handling, awareness of water conditions, and backup methods to ensure safety and effectiveness. By understanding the principles and limitations of UV disinfection, you can effectively use this technology to provide safe drinking water during outdoor adventures.
Stay tuned for the next installment in this series, where we will explore additional methods and tools for backcountry water treatment.