Foggy Bottom Water Hardness & Quality Report (2026)

Foggy Bottom, District of Columbia — one of Washington DC's most historically significant neighborhoods, home to the U.S. Department of State, the Kennedy Center for the Performing Arts, George Washington University, and the Watergate Complex along the Potomac River — receives its municipal water from DC Water (District of Columbia Water and Sewer Authority), which draws from the Potomac River at the Little Falls pumping station near Great Falls, Maryland. DC Water's McMillan Sand Filtration Site and Dalecarlia Water Treatment Plant process Potomac River water for the entire District of Columbia.

The moderately soft 83 mg/L hardness and low TDS of 143.2 mg/L reflect DC Water's effective Potomac River softening treatment. The Potomac River raw water carries moderate dissolved hardness (~120–180 mg/L) from its diverse watershed — draining the Blue Ridge Province (Catoctin greenstone, Harpers Formation quartzite, Blue Ridge granodiorite), the Valley and Ridge Province (Great Valley Ordovician limestones, Silurian and Devonian shale and limestone), and the Piedmont of Maryland and Virginia. DC Water's treatment process applies lime softening that effectively reduces the raw Potomac hardness, delivering a moderately soft finished product to Foggy Bottom and the broader District of Columbia distribution system.

At 83 mg/L, Foggy Bottom's water is moderately soft — comfortable for everyday household use. Scale forms slowly over many months, soap lathers well, and the dishwasher produces clean results. Semi-annual descaling of heating appliances is adequate. The PFAS level of 4.8 ppt is among the more favorable readings in the Washington DC metropolitan dataset — DC Water's Potomac intake at Little Falls is upstream of several major federal military and defense installations, and the District benefits from stringent federal water quality monitoring and the Potomac River Commission's active source water protection program.