Great Falls Water Hardness & Quality Report (2026)
Water Hardness
9.9 grains per gallon
Source
reservoir
pH Level
8.1
neutral = 7.0
Lead
0.007 mg/L
✓ Below action level
TDS
404.2 mg/L
Est. Daily Cost
$0.45
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In Great Falls, your appliances are currently losing 23% efficiency due to mineral buildup.
| Appliance | In Great Falls | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 4 yrs | 8.5 yrs | -53% |
| Washing Machine | 7.3 yrs | 12 yrs | -39% |
| Water Heater | 8.8 yrs | 15 yrs | -41% |
Regional Water Comparison
How Great Falls compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Great Falls, Virginia | 169 mg/L | 8.8 ppt | 🟠 Hard | reservoir |
| Wolf Trap, Virginia | 114.5 mg/L | 5.8 ppt | 🟡 Moderately Hard | reservoir |
| Reston, Virginia | 118.5 mg/L | 6 ppt | 🟡 Moderately Hard | reservoir |
| Potomac, Maryland | 113.5 mg/L | 6.1 ppt | 🟡 Moderately Hard | reservoir |
| North Potomac, Maryland | 140.5 mg/L | 7.6 ppt | 🟠 Hard | reservoir |
National Benchmark
How Great Falls compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Great Falls | 169 mg/L | 🟠 Moderate |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Great Falls's Water Unique?
Local geology and source profile
Great Falls, Virginia, in Fairfax County — a Fairfax County community adjacent to McLean and Reston on the Potomac River in north Virginia — receives its water from Fairfax Water, drawing from the Potomac River (at the Corbalis and Griffith water treatment plants, Fairfax County) through the north Virginia distribution.
The hard 169 mg/L hardness and TDS of 404.2 mg/L reflect the north Virginia Potomac River supply's moderately hard character — in the same range as other Fairfax Water communities (Reston: ~165 mg/L; McLean: ~170 mg/L). The Potomac River at the Fairfax Water intake drains the Virginia Blue Ridge — Precambrian Catoctin Greenstone (insoluble), Triassic Culpeper Basin (calcareous redbed arkose — moderate hardness contributor), Cambrian Conococheague Formation (calcareous — primary hardness contributor at this zone), and Ordovician Beekmantown Group (calcareous). The Triassic Culpeper and Cambrian-Ordovician calcareous input to the Potomac produces the hard north Virginia supply.
At 169 mg/L, Great Falls' water is hard — scale builds steadily in kettles and appliances, dishwashers benefit from rinse aid, and water heaters should be descaled annually. Monthly descaling is recommended. The PFAS level of 8.8 ppt warrants a certified reverse osmosis drinking water filter — Marine Corps Base Quantico (Prince William County — AFFF, a major northern Virginia PFAS source), Fort Belvoir (Fairfax County — AFFF), and the north Virginia Potomac corridor military-industrial PFAS complex contribute to Great Falls' elevated readings.
Geology & Source: Great Falls in Fairfax County draws from Fairfax Water on the Potomac River (Fairfax County, north Virginia) — the Potomac drains the Blue Ridge Mountains (Precambrian Catoctin Greenstone — insoluble) and Triassic Culpeper Basin (calcareous redbed arkose — moderate contributor) — Virginia Fairfax County Potomac River Triassic-Cambrian calcareous watershed produces hard water at 169 mg/L with TDS 404.2 mg/L.