Steripen Adventurer Opti™ UV water purifier water treatment removes bacteria & viruses Steripen pocket-sized UV water purifiers use ultraviolet light to destroy bacteria and protozoan cysts without the effort required by other pumps and filters. In addition, the Steripen UV sterilizers are effective against viruses, which is not the case with other systems. Essential for all adventurers, the Steripen Adventurer Opti™ UV Water Purifier features patent-pending technology: an optical sensor that tests the water to ensure safe use and effective cleaning. The revolutionary optical water sensor doubles as a built-in LED flashlight for added convenience on the go or at the campsite: press and hold the activation button for three seconds to provide light in the dark. Lightweight and mobile, ideal.