Disinfection and Flushing

Disinfection

Disinfection of drinking water has been one of the major public health advances of the 20th century by reducing outbreaks from waterborne diseases such as typhoid and cholera. There are two types of disinfection: primary and secondary. Primary disinfection achieves the desired kill or inactivation of pathenogenic bacteria, while secondary disinfection maintains a residual disinfectant to prevent microbial regrowth. There are several options available for primary disinfection. Chlorination, chloramination, ozonation and ultraviolet light are the most common. However, only chlorination and chloramination provide a secondary disinfectant. It is this that helps maintain the quality of water in the distribution system and is why more than 98 percent of water supply systems that disinfect use chlorine and/or chloramines. Disinfectants produce byproducts that have health risks, too. Generally, experts believe the risk of disease is much greater than the risks posed by the byproducts.

Currently, our water suppliers (Fairfax Water and the City of Fairfax) employ different methods of disinfection. Fairfax Water ozonates, and then chloraminates their drinking water, while the City of Fairfax chlorinates their drinking water. However, for approximately three months per year (late March through late June), Fairfax Water chlorinates their water to aid in the flushing of the water distribution system. The City of Fairfax is planning to switch disinfectants and begin using chloramines in the future (possibly a year from now).

Points to consider regarding chlorine and chloramines:

Chlorine

• Strong disinfectant

• Potentially noticeable “pool” or “chemical” taste/odor

• Dissipates readily with time and/or when water is exposed to air, including boiling

Chloramines

• Not as strong a disinfectant as chlorine
• Toxic to fish and other aquatic life in aquariums
• Does not readily dissipate with time, when exposed, or by boiling
• Forms a lower concentration of regulated disinfection byproducts
• Less noticeable taste or odor than chlorine
  

Flushing

Sources suggest that up to 25 percent of waterborne disease outbreaks each year in the United States may be traced to distribution system deficiencies. Even with this startling statistic, EPA’s Surface Water Treatment Rule considers maintenance of distribution systems the last barrier of protection prior to public consumption. A concern with distributions systems has been that they were primarily designed for public safety requirements or hydraulic objectives such as adequate fire protection, some of which may adversely impact water quality. Flushing is one of the most powerful tools available for maintaining distribution system water quality. However, flushing by itself will not correct other deficiencies or problems in the system.

What will flushing do?

Flushing can address taste and odor issues as well as discolored water. Flushing can remove accumulated debris and biofilms, restore disinfectant residual, and reduce bacterial growth in the water distribution system. Additionally, flushing provides a way to inspect the fire hydrants in the distribution system to assure they are working properly.

What won’t flushing do?

Flushing won’t affect a strong chlorine taste or odor, or dry skin complaints.

Loudoun Water has an annual water main flushing program that usually runs from late March through late June and also flushes as needed during other times of the year. Aside from assuring that sediments and other materials are removed from the pipes prior to the high use time of the year (which could stir up the sediments), the annual flushing program allows Loudoun Water to test all of the fire hydrants in our system to check for damages, leaks, or other problems in operation.