uv water system The UV light penetrates the outer cell wall of the microorganism, passes through the cell body, reaches the DNA (deoxyribonucleic acid) and alters the genetic material. The microorganisms are thereby destroyed in a non-chemical manner (Figure 1). The 254nm UV light is also used to destroy residual ozone present in a water stream. The 185nm UV light, utilized in TOC reduction applications, decomposes the organic molecules. The 185nm light carries more energy than the 254nm light. The 185nm light generates hydroxyl (OH·) free radicals from water molecules.