Molecularly Prist is kinda like soap. Part of it is attracted to water and part is attracted to oil (fuel). Its keeps the water in suspension in much higher quantities than kerosene does. The net result is two things, the fuel 'gels' at lower temperatures, (handy for unheated tanks common in small bizjets) and water does not settle in the tanks. This is where the killing bacteria myth comes from, it doesn't actually kill it, but it prevents it from forming in pools of water in the tanks.