Water hardness in Napa
4.4 gpg moderately hard
Tap water in Napa is moderately hard: 4.4 gpg (76 mg/L · 4.3 °dH · 7.6 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA2810003 (2025-07) · data checked 2026-10-19
Range across supply zones: 65–160 mg/L.
The Napa figure comes from State Water Resources Control Board lab results for the City of Napa system, using finished-water samples from three treatment-plant points. The median of 15 results from 2021 to 2025 is 76 mg/L as CaCO3 (4.4 gpg), with a range of 65.4 to 159.6 mg/L. That is moderately hard water. Scale builds slowly, and a scale inhibitor is often enough for the water heater.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 4.4 gpg |
|---|---|
| Utility | Napa, City Of |
How Napa compares
- Tap water in Napa is 51 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 1123 of 1372 in the United States (1 = hardest); 18 % of these cities have softer water.
- In California it is number 277 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Sonoma, 14 km away (3.2 gpg).
- Nearest city with clearly harder water: Vallejo, 21 km away (9.3 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Visible kettle scale every few weeks; vinegar or citric acid is enough.
- Water heater and washing machine: some long-term scale; a scale inhibitor slows it.
- Dishwasher: medium salt setting.
- Softener optional; pays off mainly with a gas boiler or tankless heater.
How much salt will you use for softening?
Optional. A scale inhibitor or a small softener protects the heater; soap savings are modest.
Descale a coffee machine or kettle about every 3 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Napa
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °dH |
| AEG / Electrolux | 2 |
| Beko | 1st |
| Hoover | S1 |
| LG | H1 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Napa water hard or soft?
It is moderately hard: 76 mg/L as CaCO₃ (4.4 gpg, 4.3 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Napa safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
How many grains per gallon is Napa water?
4.4 gpg, equal to 4.3 °dH, 7.6 °fH or 76 mg/L calcium carbonate.
What dishwasher salt setting should I use in Napa?
For 76 mg/L (4.3 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Napa?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA2810003 (2025-07). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA2810003 · Outdated figure? Tell us