After the water has been filtered down to a sub-micron level, the water then enters an ultraviolet sterilization chamber where any viruses, bacteria, mold, and other living microorganisms are bombarded with special, intense light of a specific wavelength. The UV light penetrates the wall of the organisms and attacks their DNA structure leaving the organism unable to reproduce (or "dead"). UV technology is recognized by the EPA as one of four approved methods of sterilizing water, and is preferable over the other three methods (chlorine, iodine, and distillation) due to the cost of treatment and effectiveness of UV (UV works almost instantaneously, leaving no residuals or chemicals in the water). The SWT BioMaster™ UV module operates for a full year at 30,000 microwatt seconds/cm². As a point of reference, the table below is a list of common bacteria and viruses, and the dosage required to render them harmless.