Which method is appropriate for disinfecting a newly installed water main?

The appropriate method for disinfecting a newly installed water main is the use of chlorine with a dose of 25 mg/L. Chlorine is a widely accepted and effective disinfectant in water distribution systems because it has strong bactericidal properties and residual protection against subsequent contamination. When applied correctly, chlorine can effectively eliminate pathogenic microorganisms that may be present in the water main or introduced during installation.

Chlorination is a standard practice recommended by health and safety guidelines, including those from the Environmental Protection Agency (EPA) and the American Water Works Association (AWWA). The specified dose of 25 mg/L is typically effective and provides sufficient contact time needed for disinfection.

While other methods listed may have specific applications in water treatment, they are not considered appropriate for the routine disinfection of newly installed water mains. For example, iodine might be effective in smaller applications, hydrogen peroxide is less commonly used and might not provide prolonged residual disinfection, and UV treatment generally does not offer residual protection against re-contamination after the water leaves the treatment facility.