Herndon Water Hardness & Quality Report (2026)
Water Hardness
7.8 grains per gallon
Source
reservoir
pH Level
7.9
neutral = 7.0
Lead
0.005 mg/L
✓ Below action level
TDS
274.5 mg/L
Est. Daily Cost
$0.36
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 Herndon, your appliances are currently losing 18% efficiency due to mineral buildup.
| Appliance | In Herndon | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 5.2 yrs | 8.5 yrs | -39% |
| Washing Machine | 8.6 yrs | 12 yrs | -28% |
| Water Heater | 10.2 yrs | 15 yrs | -32% |
Regional Water Comparison
How Herndon compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Herndon, Virginia | 134 mg/L | 6.9 ppt | 🟠 Hard | reservoir |
| Reston, Virginia | 118.5 mg/L | 6 ppt | 🟡 Moderately Hard | reservoir |
| Oak Hill, Virginia | 114.5 mg/L | 5.8 ppt | 🟡 Moderately Hard | reservoir |
| Sterling, Virginia | 158.5 mg/L | 8.2 ppt | 🟠 Hard | reservoir |
| Chantilly, Virginia | 183.5 mg/L | 9.5 ppt | 🔴 Very Hard | reservoir |
National Benchmark
How Herndon compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Herndon | 134 mg/L | 🟠 Moderate |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Herndon's Water Unique?
Local geology and source profile
Herndon, Virginia, in Fairfax County near Dulles International Airport in northern Virginia's technology corridor, receives its municipal water from Fairfax Water, one of the largest water utilities in Virginia. Fairfax Water draws from two principal sources: the Occoquan Reservoir — impounded on Bull Run in Prince William County — and the Potomac River via the Griffith Water Treatment Plant in Great Falls. Both sources serve the entire Fairfax County service area, with blend ratios adjusted seasonally based on reservoir levels and Potomac River quality.
The moderate 134 mg/L hardness reflects the composite character of Fairfax Water's blended supply. Occoquan Reservoir water is collected from a Piedmont Province watershed draining across Precambrian and Paleozoic metamorphic rocks (schists, gneisses, and metavolcanics) with some contact with Triassic Newark Basin sedimentary formations — producing moderately soft source water. The Potomac River at Great Falls delivers harder water (~150–170 mg/L) from its extensive Valley and Ridge tributary drainage through the Shenandoah Valley carbonate corridor in Virginia and West Virginia. The blended finished water falls in the moderate range across the Fairfax service area.
At 134 mg/L, Herndon's water is moderately hard — comfortable for everyday household use in this tech-sector community. Scale forms gradually in kettles and appliances over months, soap lathers adequately, and the dishwasher produces clean results with standard rinse aid. Quarterly descaling of kettles and coffee machines is sufficient. The PFAS level of 6.9 ppt reflects Herndon's proximity to Dulles Airport and the dense technology and defense contractor corridors of northern Virginia — a certified drinking water filter is a practical choice for daily water consumption.
Geology & Source: Herndon in Fairfax County is served by Fairfax Water drawing from Occoquan Reservoir on the Bull Run watershed and the Potomac River — the upper Occoquan watershed drains Piedmont Province metamorphic rocks with moderate carbonate contact from Triassic sedimentary intrusions — Piedmont and Valley and Ridge blended supply produces moderately hard water at 134 mg/L characteristic of Fairfax Water's Occoquan-Potomac blended system.