Ultraviolet Water Purification is what you use if you want 99.999% elimination of microorganisms from your water.
UV or Ultraviolet water sterilization is effective and can be used with city or well water. Pre-filtered water is exposed to UV light which kills viruses, bacteria, molds, yeast and other organisms. It is so effective it is used in industry and hospitals for water sterilization.
Ultraviolet is meant to be used as a post-disinfection method. In other words, after your water passes through another filter to remove contaminates and other particles, it then passes under UV to have microorganisms eliminated.