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Water Main Disinfection

Camp Archbald Main Disinfection hydrant  111513

According to AWWA standard for Disinfecting Water Mains C651-05, all new water mains must be disinfected before they can go into service. In addition, all water mains, water holding tanks, or snow melters removed from service for inspections, repairs, or other activities that could potentially cause water contamination must be disinfected before returning to service. This would include pipe breaks which induce a loss of pressure as well. Farnham & Associates, Inc. not only provides exceptional service and documentation pertaining to the procedure; we also exceed AWWA requirements for the dechlorination of the flushing process afterward and documentation of the discharged water chlorine residual.

The standard has been revised and will be published in the next several months. When it is available, a notice will be published in the official notice section of Journal – American Water Works Association. The standard becomes an effective AWWA standard on the first day of the month following such publication in Journal – American Water Works Association. Please find below a summary of the revised standard and an outline of revisions.


Camp Archbald Main Disnfection 1 111513This standard describes essential procedures for the disinfection of new and repaired potable water mains. New water mains shall be disinfected before they are placed in service. Water mains taken out of service for inspection, repair, or other activities may or may not require disinfection and sampling, depending on the risk of contamination. This standard describes the process for evaluating the risk under different conditions.


Major revisions made to the standard in this edition include the following:

  1. Clarify differences in the requirements between new and repaired mains. 
  2. Change requirement for bacteriological sampling in new mains from 2 sets of samples 24 hrs apart to add 2 options for 2 sets of samples: Option A samples are 16 hours apart and Option B samples are 15 min apart after a 16 hr rest period. 
  3. Developed a rationale for evaluating risk during pipe repairs, and the level of disinfection and sampling needed under those conditions. 
  4. Add spray disinfection method for large transmission mains. 
  5. Appendix C has been deleted, and instead a reference to C655 is made for dechlorination.