Trust your water more with the SteriPen Ultralight UV Purifier. This purifier is small enough to take on nearly any adventure, and weighs in at just 3 ounces so your bag weight stays low. This purifier is water-activated, so it automatically starts on contact. This means you won't accidentally turn it on in your pack or forget to turn it on in the water. Once on, it takes 90 seconds to purify a liter of water, and the rechargeable battery can power 20 treatments before you'll need to recharge it.