SteriPen is a water purifier that uses intense UV light to kill bacteria in water. The water can come from a tap or a natural resource like a river or lake, and works by exposing bacteria to UV light which disrupts the DNA of the bacteria, preventing it from replicating. This is a powerful tool used with many water filters, making the portable SteriPen a nice option for travelers. Inorganic solids are still a danger as drinking water may contain heavy metals such as lead and mercury. The IntelliTEC Purity Tester measures and displays the amount of Total Dissolved Solids in the water.