When camping, backpacking and hiking, if you won't have access to power for days at a time, this is the water purification system for you. The Adventurer Opti UV Water Purifier features a unique technology - an optical eye sense water to ensure safe use and effective treatments. The revolutionary optical water sensor doubles as an integrated LED flashlight for added convenience on the trail or around the campsite. Hold down the activation button for three seconds to illuminate the darkness.  Adventurer Opti is powered by two CR123 batteries making it a lightweight water purification system and keeping it operating effectively even in cold environments. Works in containers with a minimum 4.44 cm diameter opening.