"The answer? A simple and universal yes. The SteriPEN uses C Wavelength unltraviolet light (254nm) to purify water in a similar fashion to that of larger treatment facilities. The UV light actually destroys the DNA of any unwanted substance, rendering it harmless for drinking. Users pick between the ½ liter (16 ounce) and one liter (32 ounce) setting, push the button, and gently stir the pen through the water. The LCD will count down from 48 seconds (1/2 liter) or 90 seconds (1 liter), while a visible white light (with no purification purpose) gives the appearance that something is happening. Once complete, the light will turn off and a smiley face will show up on LCD screen indicating the water is safe for drinking. If the pen is pulled out before the appropriate dosage a frown will signify the water is not so safe. The pen won't activate until it is in contact with water and the UV light offers no health risk once immersed in the water. Unlike chemical options, the UV light doesn't make the water taste any different and works much faster than their up to four hour waiting period."