Water hardness in San Jose
8.8 gpg hard
Tap water in San Jose is hard: 8.8 gpg (151 mg/L · 8.5 °dH · 15.1 °fH).
Source: San Jose Water 2025 Water Quality Report (CCR), Hardness as CaCO3 secondary table (2025) · data checked 2026-10-19
Range across supply zones: 77–451 mg/L.
3 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| gpg | mg/L | ||
|---|---|---|---|
| Groundwater | 16.8 | 288 | very hard |
| Mountain Surface Water | 8.8 | 151 | hard |
| VW Surface Water (Valley Water imported) | 5.8 | 99 | moderately hard |
San Jose Water reports three supplies in its 2025 report: mountain surface water at 151 mg/L, local groundwater averaging 288 mg/L (175 to 451), and imported Valley Water surface water at 99 mg/L. Hardness therefore depends on the neighborhood, and the 151 mg/L (8.8 gpg) on this page is the median, not a typical tap. The company serves only part of the city, and other providers cover the rest.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 8.8 gpg |
|---|---|
| Utility | San Jose Water Company (investor-owned; CPUC regulated) |
How San Jose compares
- Tap water in San Jose is close to the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 703 of 1372 in the United States (1 = hardest); 49 % of these cities have softer water.
- In California it is number 185 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Milpitas, 11 km away (4.7 gpg).
- Nearest city with clearly harder water: Santa Clara, 8 km away (15.8 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Fast scale on taps, shower screens and kettle; white spots on glassware.
- Water heater: efficiency loss and element failures within years if unprotected.
- Dry skin and dull hair after showering are common.
- Softener recommended; jug or reverse osmosis for drinking.
How much salt will you use for softening?
Recommended, especially with a heater or boiler: scale cuts efficiency and shortens its life.
Descale a coffee machine or kettle about every 2 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in San Jose
| Brand | Setting for this water |
|---|---|
| Bosch | H02 |
| Miele | 8 °dH |
| AEG / Electrolux | 2 |
| Beko | 3rd |
| Hoover | S1 |
| LG | H2 |
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 San Jose water hard or soft?
It is hard: 151 mg/L as CaCO₃ (8.8 gpg, 8.5 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in San Jose 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 San Jose water?
8.8 gpg, equal to 8.5 °dH, 15.1 °fH or 151 mg/L calcium carbonate.
What dishwasher salt setting should I use in San Jose?
For 151 mg/L (8.5 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in San Jose?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Source
Source: San Jose Water 2025 Water Quality Report (CCR), Hardness as CaCO3 secondary table (2025). Method: own measurement. San Jose Water 2025 Water Quality Report (CCR), Hardness as CaCO3 secondary table · Outdated figure? Tell us