Fairfax Water provides their customers with water treated at one or two of four possible treatment plants. The James J. Corbalis Jr. and the Frederick P. Griffith Jr. Treatment Plants are owned and operated by Fairfax Water and provide water to most of the county. The Dalecarlia and McMillan Treatment Plants, part of the Washington Aqueduct, are owned and operated by the U.S. Army Corps of Engineers and provides water to the City of Falls Church and some of the surrounding area. The Corbalis Treatment Plant and the Dalecarlia and McMillan Treatment Plants treat water from the Potomac River. The Frederick P. Griffith Jr. Treatment Plant treats water from the Occoquan Reservoir. As can be seen below most of the county is served by the Fairfax Water owned water treatment plants- the blue area.
After World War II Fairfax County had over 20 small water systems that primarily operated water distribution systems. In 1957, the county supervisors created the Fairfax County Water Authority (now called Fairfax Water), to centralize the water supply, but the county did not yet have a reliable water supply and distribution system. The City of Falls Church was supplied water by the Washington Aqueduct. In 1959, Fairfax County Water Authority and the City of Falls Church signed a 30-year agreement allowing the city to deliver water to customers who were located outside the city limits in the county.
Over the years as the county grew Fairfax Water expanded its infrastructure. They built the James J. Corbalis Jr. and the Frederick P. Griffith Jr. Treatment Plants and expanded their distribution system serving over 1.7 million people with the lowest water rates in the region. Meanwhile, the City of Falls Church system (the green and brown areas) provided water to 120,000 people and was using inflated water rates to fund part of the city’s operations. In 2010 a state judge ruled that Falls Church's transfer of water utility profits to their General Fund was an unconstitutional tax on people who lived outside the boundaries of the city. The decision blocked all future transfers, and after appeals, mediation and action by the county supervisors resulted in an agreement for Falls Church to sell its water system to Fairfax County which was ratified by the voters in 2013. The deal required that the high city water rates be lowered to county levels within two years.
The result is that now Fairfax Water provides water to county residents from their two water treatment plants and buy water from the Washington Aqueduct to supply residents in and around the City of Falls Church. The newer developments around Merrifield and the Dunn Loring Metro Station are supplied water from the Fairfax Water owned plants. Water rates and hookup charges throughout the county are now level and undoubtedly, Fairfax Water will provide any expanded water service from their own water treatment plants. Though, both the Washington Aqueduct and Fairfax Water run excellent water treatment plants.
In order to ensure that tap water is safe to drink, the EPA limits the amount of certain contaminants (a list of more than 90 contaminants) that can be in the water provided by public water systems under the Safe Drinking Water Act. When untreated water enters the treatment plants, coagulants are added to cause small particles to adhere to one another and settle in a sedimentation basin. The water is then filtered through activated carbon and sand to remove remaining fine particles. This produces water with extremely low turbidity and provides excellent barrier against pathogens such as Cryptosporidium and Giardia. Next, the water is disinfected with chlorine to kill harmful bacteria and viruses. A corrosion inhibitor is added to help prevent leaching of lead and copper that might be in household plumbing or service laterals. Fluoride is added to protect teeth. Powdered activated carbon and potassium permanganate may also be added to the treatment process to remove taste or odor-causing compounds. In addition to these treatment steps, the Corbalis and Griffith plants use ozone to further reduce odors and organic material.
The quality of the water being produced at Washington Aqueduct and Fairfax Water is excellent. It meets or exceeds all United States Environmental Protection Agency (US EPA) standards and requirements. The water quality report release at the end of 2016 covers the sampling done during calendar year 2015. There were no violations of the U.S. EPA’s Safe Drinking Water Act and you can view the report at this link.