Standard Article

Chlorine Residual

Water Quality Control

  1. Linda S. Andrews

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.wq186

Water Encyclopedia

Water Encyclopedia

How to Cite

Andrews, L. S. 2005. Chlorine Residual. Water Encyclopedia. 2:398–399.

Author Information

  1. Mississippi State University, Biloxi, Mississippi

Publication History

  1. Published Online: 15 JUL 2005


Chlorine is a disinfectant added to drinking water to control microbial contamination. Both commercial water bottlers and public water systems use chlorine for this purpose. Levels added are calculated to maintain a disinfectant (chlorine) residual throughout the distribution system from the treatment facility to the end user. Chlorine may be applied as chlorine gas, hypochlorite solutions, or other chlorine compounds in solid or liquid form. Hypochlorous acid present in aqueous chlorine solutions is the biocidal “active chlorine.” In recent years, some health concerns have developed over the discovery of potentially carcinogenic by-products generated during chlorination in the presence of organic material. Continuous chlorination is a necessity for surface water supplies from lakes, springs, ponds, or cisterns, and it typically uses a chlorine residual of 3–5 ppm. Higher levels of chlorine residual may cause an objectionable flavor and odor. Many health risks are associated with water that has not been disinfected, and health risks are associated with total residual chlorine.


  • chlorine residual;
  • chlorine;
  • disinfectant;
  • chlorination;
  • dechlorination