Abstract: A method and apparatus for disinfecting the interior of pipelines and conduits, particularly water mains. Ozone is utilized as the disinfectant vehicle to neutralize microbial contamination of the conduit. An ozone generation system includes a venturi injector for introducing ozone into pressurized water to provide a treating solution that is introduced into and that flows along a predetermined length of the conduit to be treated. The ozone concentration is regulated to maintain an ozone residual at the conduit outlet of about 0.1 mg/L to about 0.2 mg/L for a time sufficient to assure the desired level of disinfection of the conduit interior.