San Diego
San Diego, United States has an estimated water hardness of 217 ppm (mg/L as calcium carbonate), which is classed as very hard. High scale risk. Configure appliances and descale regularly.
San Diego water hardness in every unit
| Unit | Reference estimate |
|---|---|
| mg/L or ppm (CaCO₃) | 217 |
| mmol/L | 2.17 |
| German degrees (°dH) | 12.16 |
| French degrees (°fH) | 21.7 |
| Clark degrees (°e) | 15.22 |
| Grains per US gallon (gpg) | 12.68 |
Published range: 145–243 ppm.
How the San Diego figure was derived
- Period covered: 2025-01-01 – 2025-12-31
- Calculation: The average is the simple, unweighted mean of the published values for 4 sources. The range runs from the lowest to the highest of those values.
Where San Diego's water comes from
- Supplier: City of San Diego Public Utilities Department
- Source: Treated water purchased from a wholesale supplier plus the City’s Alvarado, Miramar and Otay treatment plants
- Official website: City of San Diego Public Utilities
The City’s 2025 report lists average hardness of 237 mg/L for purchased treated water, 242 mg/L (Alvarado), 243 mg/L (Miramar) and 145 mg/L (Otay). Which source supplies you depends on your neighbourhood. City of San Diego: 2025 Annual Drinking Water Quality Report (checked 2026-10-31).
Hardness by supply zone in San Diego
| Supply zone | ppm |
|---|---|
| Purchased treated water | 203–270 |
| Alvarado | 200–285 |
| Miramar | 201–271 |
| Otay | 54–232 |
How San Diego compares
With a reference estimate of 217 ppm, San Diego ranks 10th hardest of the 69 cities in our directory, 143 ppm above the directory median of 74 ppm. Among the cities in our directory in North America, San Antonio is the hardest at 299 ppm and Portland is the softest at 9 ppm.
What the range means
Published figures for San Diego run from 145 to 243 ppm. That is a wide spread (98 ppm), so the figure at your own tap could differ a lot from the average. Supply zones, blending of different water sources, and the time of year can all move it. A test strip or your utility's postcode lookup is worth the extra step here.
What very hard water means at home
Very hard water forms scale quickly on heating elements and in pipework, shortens the interval between descaling, and often leaves visible marks on glass and tiles. Appliance-level protection (salt, filters, scheduled descaling) is worth the effort, and some households consider a whole-home softener.
Using a 217 ppm reading with your appliances
- Dishwasher: salt check manual; match the converted reading to your model. Use salt only as specified for the built-in softener.
- Coffee machine: descale when the manual or machine indicates; filter: use only a compatible filter specified by the manufacturer.
- Laundry: use the hard-water dose. Use the label maximum only for large or heavily soiled loads.
- Kettle: Inspect for scale; follow the manual.
- Humidifier: For ultrasonic or impeller units, use low-mineral water such as distilled water. Empty and dry portable tanks daily; clean every third day. Follow manufacturer instructions.
Official manufacturer guidance
Use these references with your exact appliance model. They explain settings and maintenance, not the local water measurement. Source languages and model limits are shown; these are not affiliate links.
- Bosch US — Dishwasher salt and the low-salt indicator (en-US)
Salt and scale guidance for dishwashers equipped with a salt reservoir; it does not mean every US dishwasher uses salt.
- Bosch US — How to clean and descale Bosch dishwashers (en-US)
Cleaning and descaling procedures for Bosch dishwashers, with care-product instructions.
(checked 2026-10-20).
Hardness alone does not determine maintenance frequency. How to match your reading to an appliance manual. Dishwasher settings by brand: find your setting. Thinking about a softener? Pros and cons and sizing. Kettles and coffee machines: descaling guide. Portable humidifier care: US EPA guidance.
Frequently asked questions
Do I need dishwasher salt in San Diego?
Check manual. Use salt only as specified for the built-in softener. Always follow your dishwasher manual.
How often should I descale a coffee machine in San Diego?
Descale when the manual or machine indicates. Hardness alone does not determine an interval: usage and appliance design also matter. Water filter: use only a compatible filter specified by the manufacturer.
Do I need a water softener in San Diego?
It is worth considering. At this level scale builds quickly, so a softener or filter system can reduce descaling and protect appliances. Check your appliance manuals first, as some limit softened-water use.
Is hard water in San Diego safe to drink?
Water hardness is mainly an aesthetic and scale issue. The World Health Organization does not set a health-based guideline value for it. Hardness affects taste, scale and detergent use rather than drinking safety, and your utility is responsible for meeting drinking-water standards. If you have a specific health or dietary concern, ask your doctor.
How to check your own water
City averages are a starting point. To get your actual figure, check the linked source (City of San Diego: 2025 Annual Drinking Water Quality Report) and obtain a current report for your address from your water supplier, or dip a hardness test strip in a glass of cold tap water and read it against the chart. Strips usually report in °dH, gpg or ppm; enter the number into the Waterdial checker to convert it and see the matching appliance settings. Use a recent, correctly performed hardness test when a city estimate is too broad.
Source
City of San Diego: 2025 Annual Drinking Water Quality Report, checked 2026-10-31. Guidance is general; your appliance manual takes priority.
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