The SteriPEN Classic Safe Water System Pack comes with everything you need for your outdoor adventures. The System Pack includes the SteriPEN Classic, Pre-Filter and a Nalgene BPA-Free wide-mouth water bottle. The Pre-Filter’s 40×40 micron screen fits snugly on the wide-mouth water bottle, protecting the drinking threads, and removing particulates while allowing clear water to flow into the bottle. SteriPEN Classic’s tapered end provides a snug fit with water bottles and with the SteriPEN Pre-Filter for wide-mouth water bottles, you have a reliable water purification system. Four AA batteries power the UV lamp that keeps working for 8,000 treatments so you know you’ll have safe drinking water far into the future. When camping, hiking, backpacking or traveling the Classic with Pre-Filter pack is the perfect complement to a wide-mouth one liter water bottle. The 40×40 micron screen Pre-Filter fits perfectly on wide-mouth one liter water bottles and removes particulates that can get in the way of UV light in water. The Pre-Filter is designed to be stored directly on the wide mouth bottle and the SteriPEN Classic fits perfectly in the filter. Just insert Classic in the filter open, turn the bottle upside down, and gently rock to circulate light throughout bottle.