Used it once on my sink water to test, never got into using it. I'll even throw in the spare batteries I bought for it.

Easy to use—press button to activate, place in water and stir; lamp turns off and an indicator signals when water is purified Ultraviolet UV-C light rays safely sterilize clear water by destroying 99.99% of protozoa, including Giardia, Cryptosporidia, bacteria and even viruses Protects you from risks that cause botulism, cholera, dysentery and typhoid, just to name a few Optical sensor doubles as a convenient LED flashlight Retail package includes 2 non-rechargeable (disposable) CR123 batteries and a neoprene case with belt loop Device works with containers with minimum 1.75 in. diameter opening (i.e. Nalgene wide-mouth bottles) One set of CR123 batteries will treat up to 50 liters of water UV lamp life: 8,000 treatments Small and lightweight, weighing just 3.8 oz. with batteries Recipient of Backpacker Magazine's 2011 Editors' Choice Award