Standard Article


Municipal Water Supply

  1. Rasheed Ahmad

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.mw41

Water Encyclopedia

Water Encyclopedia

How to Cite

Ahmad, R. 2005. Dechlorination. Water Encyclopedia. 1:169–170.

Author Information

  1. Khafra Engineering Consultants, Lilburn, Georgia

Publication History

  1. Published Online: 15 JUL 2005


Dechlorination is the practice of removing all or a specified fraction of total residual chlorine. In potable water practice, dechlorination is used to reduce the residual chlorine to a specified level at a point where the water enters the distribution system. Dechlorination has been beneficial for waters that are burdened with high concentrations of ammonia nitrogen and organic nitrogen. In some cases where taste and odor control is a severe problem, control is achieved by complete dechlorination, followed by rechlorination. This removes the taste-producing nuisance residuals and prevents the formation of nitrogen trichloride (NCl3) in the distribution systems. Dechlorination of wastewater and power plant cooling water is required to eliminate residual chlorine toxicity, which is harmful to the aquatic life in the receiving waters. Other special applications requiring dechlorination are ahead of demineralizers, boiler makeup water, certain food plant operations, bottled water, and the beverage industry. In these cases, the dechlorination process is arranged to remove all residual chlorine.


  • dechlorination;
  • chlorination;
  • free chlorine;
  • combined chlorine;
  • aeration;
  • granular activated carbon (GAC);
  • sulfur dioxide;
  • taste and odor control;
  • residual chlorine