The effect of UV light on bacteria, viruses, spores and moulds has been known to science for many years. The shortwave ultraviolet energy is lethal to micro-organisms as the UV rays penetrate the cell membranes and destroy the DNA inside the cell, effectively destroying the organism and it’s ability to reproduce. Ultraviolet disinfection is extremely fast, it requires no chemicals or additives and cannot be overdosed. No chemical residuals are left in the treated water. The UV intensity (dose) is measured in mJ/cm2. For domestic situations UV systems should give at least 30 mJ/cm2 and for larger industrial systems 40 mJ/cm2. The dose required to inactivate bacteria depends on the bacteria. The higher the dose of UV the more of each bacteria are killed.