Potomac River

River · Mid-Atlantic

Serves 10 cities in our database · ~4,418,462 residents

77
Avg Hardness (PPM)
8.9
Avg PFAS (ppt)
1.6
Avg Lead (ppb)
10
Cities Served
Soft
0Slightly
60Moderate
120Hard
180Very Hard
250Extreme
400+
77 PPM Moderately Hard
CONTAMINANT LEVELS Hardness 77 PPM TDS 128 PPM PFAS 8.9 ppt Lead 1.6 ppb Chlorine 1.2 mg/L Nitrate 1.1 mg/L

About Potomac River

The Potomac River supplies drinking water to the Washington D.C. metropolitan area, including parts of Maryland and Virginia. The river has undergone a dramatic environmental recovery since the 1960s when it was declared a national disgrace.

Geography & Hydrology

The Potomac flows 405 miles from the Appalachian highlands to the Chesapeake Bay. The Washington Aqueduct, operated by the US Army Corps of Engineers, has drawn water from the Potomac since 1859.

How Potomac River Water Is Treated

The Washington Aqueduct uses conventional treatment plus granular activated carbon. The Dalecarlia and McMillan treatment plants process about 180 million gallons per day for D.C. and parts of northern Virginia.

Across the 10 cities we track, water from Potomac River averages 77 PPM hardness (Moderately Hard), ranging from 38 to 120 PPM. This is relatively soft water - a water softener is generally not needed.

PFAS concern: Cities supplied by Potomac River average 8.9 ppt PFAS, exceeding the 2024 EPA limit of 4 ppt. An NSF P473 certified filter is recommended for drinking water.

Current Challenges

Agricultural runoff from the Shenandoah Valley, urban stormwater from the metro area, combined sewer overflows in D.C. during heavy rain, and PFAS from upstream military installations and firefighting foam use.

Cities Supplied by Potomac River

Water quality varies by city due to local treatment, distribution infrastructure, and source blending.

Germantown, MD

58 PPM · Slightly Hard 1,900,000 residents

Gaithersburg, MD

110 PPM · Moderately Hard 1,900,000 residents

Arlington, VA

38 PPM · Slightly Hard 215,000 residents

Alexandria, VA

39 PPM · Slightly Hard 159,200 residents

Stafford, VA

100 PPM · Moderately Hard 123,684 residents

Rockville, MD

61 PPM · Moderately Hard 52,000 residents

Cumberland, MD

80 PPM · Moderately Hard 27,039 residents

Herndon, VA

110 PPM · Moderately Hard 24,601 residents

Washington, DC

120 PPM · Hard 15,690 residents

Silver Spring, MD

55 PPM · Slightly Hard 1,248 residents

Recommended for Potomac River Water

Based on average water quality across 10 cities supplied by Potomac River.

PFAS Filter Clearly Filtered Pitcher ~$90 Test Your Tap Home Water Test Kit ~$30

Affiliate disclosure: we may earn a commission on purchases. Recommendations based on water quality data.

Frequently Asked Questions

Is Potomac River water safe to drink?
Water from Potomac River meets EPA safety standards in all served cities. However, average PFAS levels of 8.9 ppt exceed the 2024 EPA health guideline. A certified water filter is recommended for drinking water.
Why is Potomac River water soft?
Potomac River benefits from source geology that produces naturally soft water with low dissolved mineral content.
How many people drink Potomac River water?
Potomac River supplies drinking water to 10 cities in our database, serving approximately 4,418,462 residents. The largest cities include Germantown, MD; Gaithersburg, MD; Arlington, VA.
Do I need a water filter for Potomac River water?
Yes. With PFAS averaging 8.9 ppt, a reverse osmosis or activated carbon filter is recommended. Look for NSF P473 certification.