Where Does Your Water Actually Come From in the DMV?
Northern Virginia, DC, and suburban Maryland don't all draw from the same source, and that changes what's actually in your water.
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Turn on a tap anywhere in the DMV and the water traveled a different path to get there depending on exactly where you live.
Washington, DC and much of Northern Virginia
DC's water, along with a large share of Fairfax Water's service area (which also reaches Alexandria, Prince William, and Loudoun through wholesale agreements), is drawn primarily from the Potomac River. Fairfax Water also uses the Occoquan Reservoir as a second source for its southern service area.
Suburban Maryland
WSSC Water, serving roughly 1.9 million people across Montgomery and Prince George's counties, draws from two different rivers depending on location: the Potomac River, treated at the Potomac Water Filtration Plant near Swain's Lock, and the Patuxent River. Which one supplies your home actually changes your water's mineral content. Potomac water runs harder, Patuxent water runs noticeably softer.
Groundwater communities
Not every DMV community relies on a river at all. Some towns, like Poolesville, MD, rely on local groundwater wells for their municipal supply rather than surface water, which brings a different set of considerations, like iron and mineral content tied to local geology.
Why the source matters to you
Source water determines baseline hardness, seasonal variation, and what a utility has to treat for before it ever reaches your home. Two houses a few miles apart, on different systems, can have meaningfully different water, which is exactly why a system sized around a generic average often under- or over-treats what's actually coming out of your tap.
