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Water Quality in Northern Virginia


Clean water is essential to human life and the health of the environment. There are several types of waterbodies in Northern Virginia. These include tidal rivers, bays, and wetlands as well as non-tidal rivers, streams, creeks, wetlands, lakes and ponds.  Groundwater in the Piedmont zone typically occurs deep underground in fractured bedrock aquifers. In the Coastal zone, groundwater occurs in shallower, sand and gravel aquifers. The entirety of Northern Virginia falls within the Chesapeake Bay Watershed.

Water quality is defined by its physical, chemical, biological, and aesthetic (appearance and smell) characteristics. A healthy aquatic ecosystem is one in which the water quality is not impaired and supports a rich and varied community of microbes, plants, and animals.

Why is water quality important?

Water quality in a body of water influences the way in which communities can use the water for activities such as drinking, swimming, fishing, irrigation, or commercial purposes. In Northern Virginia, water resources provide major environmental, social, cultural, and economic value to communities.  If water quality is not maintained and becomes degraded, it is not just public health that will suffer. The ecological, commercial, and recreational value of our water resources will also diminish.


Surface water from the Potomac River and the Occoquan Reservoir the major sources of drinking water for Northern Virginia. The City of Manassas draws surface water for its residents from Lake Manassas, an impoundment of Broad Run. The City of Fairfax also provides public drinking water to customers in eastern Loudoun County (as well as to its residents) through reservoirs on Goose Creek.


What affects the quality of our water?

Water quality is closely linked to the surrounding environment and land use. Impaired water bodies are those that do not meet statutory water quality standards and designated uses, and thus do not support aquatic life and wildlife, fish and shellfish consumption, are not suitable for recreational use by humans, or do not meet public water supply standards.

Water quality can be impaired by intensive agriculture, urban and suburban use, and industry. The modification of natural stream flows by dams can also affect water quality. The weather, too, can have a major impact on water quality, particularly when there is a drought which decreases stream flow or heavy precipitation events that result in high levels of storm water runoff.

Groundwater is also an integral part of our water supply. Groundwater maintains base flow in perennial rivers and streams. In some suburban and rural areas of Northern Virginia that are not connected to the municipal water supply, groundwater wells supply water to the homes and farms. Like other bodies of water, groundwater that is close to urban or industrial development is vulnerable to contamination.

Generally, the water quality of rivers is best in the headwaters. Water quality frequently declines as rivers flow downstream through regions where more land is covered with impervious surfaces and pollution from intensive agriculture, towns, cities and industry increases.

Stormwater, which can also carry heavy loads of nutrients, bacteria, organic matter and other pollutants, finds its way into streams and rivers, mostly via the stormwater drain network and, ultimately, discharging it into the Chesapeake Bay.

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How is water quality measured?

Water quality is routinely monitored at many locations throughout Northern Virginia. Federal and state statutes (Clean Water Act, 1972; Water Quality Monitoring, Information, and Restoration Act (VA Code 62.1-44.19-5), 1997) require the Virginia Department of Environmental Quality (VDEQ) and the Virginia Department of Conservation and Recreation (VDCR) to monitor and assess water quality in Virginia, and to identify and report to the U.S. Environmental Protection Agency on water bodies that are impaired. The presence of contaminants and the characteristics of water samples are used to indicate the quality of water. Samples from the mud at the bottom of lakes and rivers also are tested for the presence of pesticides and other harmful compounds. Water quality indicators that are commonly monitored include:

  • Biological: bacteria, algae

  • Physical: temperature, turbidity and clarity, color, salinity, suspended solids, dissolved solids

  • Chemical: pH, dissolved oxygen, biological oxygen demand, nutrients (including nitrogen and phosphorus), organic and inorganic compounds

  • Aesthetic: odors, color, floatables


Measurements of these indicators can be used to determine, and monitor changes over time in water quality, and determine whether it is suitable for the health of the natural environment and the uses for which the water is required. VDEQ’s monitoring and assessment efforts are published biennially. This water quality information can then be used to develop management programs and action plans to ensure that water quality is protected.


What can be done to protect water quality?

Luckily there are many things that can be done to protect and maintain water quality in Northern Virginia and the Clean Water Partners have developed many resources to educate residents on what they can do.  Visit our Tips to Reduce Pollution and Runoff to get some ideas!

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