Disinfection should be monitored to ensure appropriate dose of disinfectant and disinfection efficacy. Depending on the application process and the pathogenic agent of concern, this may be done in different ways. Examples include measurement of the active agent (e.g. residual chlorine levels), indirect measurement of the active agent by an indicator process (e.g. monitoring oxygen reduction potential), and measuring efficacy using indicator bacteria (e.g. heterotrophic bacteria plate counts).