Is DC, Maryland, or Virginia Tap Water Hard? Here's What the Utilities Report
Every major DMV utility reports its water as moderately hard to hard, but the exact number depends on which system serves you.
Ask three DMV utilities how hard their water is, and you'll get three different answers, because hardness depends on the specific source and geology feeding each system.
Washington, DC
DC's water, drawn from the Potomac River, generally falls in the moderately hard range, and tends to run harder during warmer months when the Potomac's mineral concentration rises with lower flow.
Northern Virginia (Fairfax Water)
Fairfax Water's own published FAQ describes its water as "moderately hard to hard," in the range of 5 to 10 grains per gallon, or 84 to 170 mg/L, depending on whether an area is served primarily by the Potomac River or the Occoquan Reservoir, and on seasonal rainfall. Fairfax Water's service area extends into Alexandria, and reaches Prince William and Loudoun County through interconnection agreements.
Suburban Maryland (WSSC)
WSSC Water's own guidance draws the clearest contrast in the region. Potomac River water, which it treats at its Potomac plant, averages roughly 120 to 130 mg/L of dissolved calcium and magnesium, solidly hard. Patuxent River water, treated separately, averages closer to 60 to 65 mg/L, notably softer. Which one reaches your tap in Montgomery or Prince George's County depends on which treatment plant serves your specific area.
What this means practically
For reference, the Water Quality Association classifies water as hard starting around 7 grains per gallon, about 120 mg/L. Most of the DMV sits at or above that line for at least part of the year, which is why scale buildup, spotted glassware, and shortened water heater life are such common complaints across the region, almost regardless of exactly which utility serves a given block.
