This standard presents essential procedures for the disinfection of new and repaired potable water mains. All new water mains shall be disinfected before they are placed in service. All water mains taken out of service for inspection, repair, or other activities that might lead to contamination of water shall be disinfected before they are returned to service. Topics covered include forms of chlorine disinfection, a description of the disinfection procedure, preventive and corrective measures during construction, methods of chlorination, final flushing, bacteriological testing, redisinfection, final connections to existing mains, disinfection procedures when cutting into or repairing existing mains, and special procedures for caulked tapping sleeves. Appendices cover chlorine residual testing, chlorine dosages, and disposal of heavily chlorinated water. The major revision in this edition of ANSI/AWWA C651-99 includes the following: the format has been changed to AWWA standard style.