Water Main Flushing Program

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Fire Hydrant Nutley Property Yard - heroTo help maintain a high standard of water quality and ensure proper and efficient fire hydrant operation, the Town of Vienna flushes water mains in its distribution system each spring.  In 2024, flushing will take place March 25-May 6 from 9 p.m.-5 a.m. 

Temporary change to treatment with free chlorine

The Town's flushing program happens at the same time that Fairfax Water Authority switches from chloramines to free chlorine for water treatment during a brief period each year.  This allows Vienna and others in the Fairfax Water service area to perform annual fire hydrant flushing.

During most of the year, chloramine, also known as combined chlorine, is added to the water as the primary disinfectant.  During the flushing program period, chlorine is added in an uncombined state, commonly referred to as free chlorine.  Free chlorine is somewhat more volatile than combined chlorine, which allows it to react with sediments suspended during flushing.

Water mains are flushed by opening fire hydrants and allowing the water to flow freely for a short period of time.  This also enables the Town to test and perform routine maintenance on the more than 800 fire hydrants within its service area.

The use of free chlorine for this short period of time also helps control biological film, known as biofilm, which is found in all water pipes and can lead to water quality problems if not controlled.  By switching to free chlorine, the biofilm is “shocked” and weakened.

What customers can expect 

Depending on your usage patterns and location within the distribution system, it may take up to a week for your drinking water to transition from combined to free chlorine or from free chlorine back to combined chlorine at the conclusion of the disinfection chemistry change period.

During the time that free chlorine is used, you may notice a chlorine taste and odor in your drinking water.  If you are especially sensitive to the taste and odor of chlorine, try keeping an open container of drinking water in your refrigerator.  This allows the chlorine to dissipate, thus reducing the chlorine taste.

Note:  If you have an aquarium or pond, always test the water you add to your aquatic environment throughout the year to ensure that it is free of chlorine before adding fish or other animals.  Chemical additives that remove either free chlorine or chloramines from water for use in fish tanks or ponds are available at pet/fish supply stores. 

Flushing may result in some discoloration and the presence of sediment in your water. These conditions are not harmful and should be of short duration.  If you encounter discolored water in your home, run the cold-water faucet until the water is clear.  

Report illegal use of fire hydrants

Any use of a fire hydrant can cause discoloration or sediment in the water lines.  If you suspect someone is using a fire hydrant illegally, please notify the police immediately at 703-255-6366.