Ultraviolet (UV) disinfection occurs when radiation penetrates the cell walls of microorganisms and kills both bacteria and viruses.  In order for UV light to reach the bacteria, the wastewater must be relatively clear and free of solids.  UV light is not a chemical agent and therefore produces no toxic residuals.  Once only a common large-scale application, UV light is becoming more cost-effective and widely used for small-scale applications. 

(We hope to demonstrate that the water is clean enough without using the UV light, but for now, regulatory practices require “assurances of disinfection.”)