What is temporary change in disinfectant (TCD)?

TCD is a proactive effort by the NTMWD and its customer cities to assist in cleaning city water distribution systems. This annual maintenance is performed once per year for a period of 28 days. During the rest of the year, NTMWD uses a mixture of chlorine and ammonia, called chloramine, for continued disinfection in city distribution systems. During chlorine maintenance, pure chlorine is used instead. It is a stronger disinfectant than chloramine, that effectively eliminates potentially harmful microorganisms that may exist inside distribution pipes. By performing TCD in early spring, NTMWD can reduce the growth of potentially harmful microorganisms, which can flourish during summer heat. NTMWD maintains the same concentration of chlorine in drinking water during TCD that it does of chloramines the rest of the year. By its nature, the chlorine presents a stronger taste and odor than chloramines.

Cities may supplement chlorine maintenance with aggressive distribution line flushing. During flushing, treated water is released from fire hydrants to allow microorganisms to be pulled out by high-velocity water. The downside of flushing is that it uses a lot of water and works against water conservation goals.

Show All Answers

1. What is temporary change in disinfectant (TCD)?
2. What is a "chlorine burn" and is it different than "chlorine maintenance" or "TCD"?
3. Can you reduce the amount of chlorine in the water so the taste and odor isn’t as noticeable and disinfection byproducts (DBPs) are reduced?
4. What are disinfection by-products (DBP)?
5. Does Allen comply with DBP limits? How do we know tests are accurate?
6. Does our water system contain any lead pipes?
7. How does Allen regulate levels of lead and copper?
8. Where can I learn more about lead and copper in drinking water?
9. Where does the list of regulated contaminants and allowed concentration limits or ranges come from?
10. How are new contaminants selected for the list of contaminants and how are the limits established?