Mill Valley Water Hardness & Quality Report (2026)
Water Hardness
7.4 grains per gallon
Source
mixed
pH Level
7.9
neutral = 7.0
Lead
0.006 mg/L
✓ Below action level
TDS
343.3 mg/L
Est. Daily Cost
$0.34
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 Mill Valley, your appliances are currently losing 17% efficiency due to mineral buildup.
| Appliance | In Mill Valley | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 5.4 yrs | 8.5 yrs | -36% |
| Washing Machine | 8.9 yrs | 12 yrs | -26% |
| Water Heater | 10.6 yrs | 15 yrs | -29% |
Regional Water Comparison
How Mill Valley compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Mill Valley, California | 126 mg/L | 5.7 ppt | 🟠 Hard | mixed |
| Larkspur, California | 109 mg/L | 5.2 ppt | 🟡 Moderately Hard | mixed |
| San Rafael, California | 49.5 mg/L | 3.5 ppt | 🟢 Soft | mixed |
| San Anselmo, California | 153.5 mg/L | 6.5 ppt | 🟠 Hard | mixed |
| Parkside, California | 184.5 mg/L | 7.4 ppt | 🔴 Very Hard | mixed |
National Benchmark
How Mill Valley compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Mill Valley | 126 mg/L | 🟠 Moderate |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Mill Valley's Water Unique?
Local geology and source profile
Mill Valley, California, in Marin County — a Marin County city adjacent to Corte Madera and Sausalito on the slopes of Mount Tamalpais in northwest California — receives its water from the Marin Municipal Water District (MMWD), drawing from Alpine Lake and Kent Lake (Marin County) through the north Bay Area distribution.
The moderately hard 126 mg/L hardness and TDS of 343.3 mg/L (TDS elevated relative to hardness — reflecting possible MMWD mixed supply blend including SFPUC water or Marin's slightly more mineralized Lagunitas Creek watershed sources) reflect the north Bay Area Marin supply's character — harder than the pure Franciscan Complex supply would suggest. The Marin watershed at Marin County drains the Coast Ranges — Mesozoic Franciscan Complex mélange (insoluble chert and greywacke), Cretaceous Great Valley Sequence (slightly calcareous), and Quaternary alluvium (slightly calcareous — primary hardness contributor).
At 126 mg/L, Mill Valley's water is moderately hard — scale builds in kettles and appliances over months, dishwashers benefit from rinse aid, and faucet aerators need periodic cleaning. Quarterly descaling is appropriate. The PFAS level of 5.7 ppt warrants a certified drinking water filter — Hamilton Air Force Base (Marin County — AFFF legacy site) and the north Bay Area Marin County coastal corridor contribute to Mill Valley's readings.
Geology & Source: Mill Valley in Marin County draws from the Marin Municipal Water District on Alpine Lake and Kent Lake (Marin County, northwest California) — the Marin watershed drains the Coast Ranges (Mesozoic Franciscan Complex — insoluble chert and greywacke, Cretaceous Point Reyes Conglomerate — insoluble) — California Marin County Marin watershed Coast Ranges Franciscan Complex insoluble watershed produces moderately hard water at 126 mg/L with TDS 343.3 mg/L.