Water hardness in Los Altos
18.1 gpg very hard
Tap water in Los Altos is very hard: 18.1 gpg (310 mg/L · 17.4 °dH · 31 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA4310001 (2026-01) · data checked 2026-10-19
Range across supply zones: 260–420 mg/L.
The figure is for California Water Service, Los Altos Suburban district, from State Water Resources Control Board lab results. The median of 41 results from 2021 to 2026, taken at 20 well points, is 310 mg/L as CaCO3 (18.1 gpg), with a range of 260 to 420 mg/L. This is very hard water. Scale builds fast, and a softener is worth considering.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 18.1 gpg |
|---|---|
| Utility | Cwsc Los Altos Suburban |
How Los Altos compares
- Tap water in Los Altos is 100 % harder than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 219 of 1372 in the United States (1 = hardest); 83 % of these cities have softer water.
- In California it is number 40 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Palo Alto, 5 km away (11.4 gpg).
- Nearest city with clearly harder water: Patterson, 84 km away (22.7 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Severe scale: heater elements and washing-machine heaters fail early.
- Detergent use is very high; taps and screens coat within days.
- Dishwasher at maximum salt setting.
- An ion-exchange softener is practically essential; RO for drinking water.
How much salt will you use for softening?
Yes. At this hardness a softener pays for itself through appliance life and detergent.
Descale a coffee machine or kettle about every 1 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Los Altos
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 17 °dH |
| AEG / Electrolux | 4 |
| Beko | 5th |
| Hoover | S3 |
| LG | H3 |
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 Los Altos water hard or soft?
It is very hard: 310 mg/L as CaCO₃ (18.1 gpg, 17.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Los Altos 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 Los Altos water?
18.1 gpg, equal to 17.4 °dH, 31 °fH or 310 mg/L calcium carbonate.
What dishwasher salt setting should I use in Los Altos?
For 310 mg/L (17.4 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Los Altos?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA4310001 (2026-01). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA4310001 · Outdated figure? Tell us