Yokohama
Yokohama, Japan has an estimated water hardness of 59 ppm (mg/L as calcium carbonate), which is classed as soft. Low scale risk. Use the lower end of detergent guidance.
Yokohama water hardness in every unit
| Unit | Reference estimate |
|---|---|
| mg/L or ppm (CaCO₃) | 59 |
| mmol/L | 0.59 |
| German degrees (°dH) | 3.31 |
| French degrees (°fH) | 5.9 |
| Clark degrees (°e) | 4.14 |
| Grains per US gallon (gpg) | 3.45 |
Published range: 45–72 ppm.
How the Yokohama figure was derived
- Period covered: 2025-04-01 – 2026-03-31
- Calculation: The average is the figure the source publishes for this period.
Where Yokohama's water comes from
- Supplier: Yokohama City Waterworks Bureau
- Source: Five source systems, including the Sagami Lake and Doshi River systems, treated at three purification plants
- Official website: Yokohama City Waterworks Bureau
The Bureau’s fiscal 2025 report lists citywide tap-water hardness of 45 to 72 mg/L with a mean of 59 mg/L. Yokohama City Waterworks Bureau: Water Quality Test Annual Report, fiscal 2025 (checked 2026-10-31).
How Yokohama compares
With a reference estimate of 59 ppm, Yokohama ranks 40th hardest of the 69 cities in our directory, 15 ppm below the directory median of 74 ppm. Among the cities in our directory in Asia, Shizuoka is the hardest at 80 ppm and Nagoya is the softest at 19 ppm.
What the range means
Published figures for Yokohama run from 45 to 72 ppm. The spread is relatively narrow (27 ppm), so the average is a reasonable guide, though your own tap can still differ from the citywide figure.
What soft water means at home
Soft water rarely leaves visible scale. Kettles, taps and shower screens stay clearer for longer, and detergents lather easily, so the main risk is overdosing. Start at the minimum amount on the pack and increase only if results are poor.
Using a 59 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 soft-water dose. Start at the label minimum and adjust for soil level.
- 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.
- De’Longhi Japan — ディナミカ ECAM35015BH：使い方・お手入れ (ja)
ECAM35015BH commercial coffee-machine page with a water-hardness checker listed and linked cleaning/descaling demonstrations. Model-specific, not a general household maintenance schedule.
- Panasonic Japan — 加湿機：サポート・お手入れ (ja)
Panasonic humidifier support and manual links. This manufacturer specifies fresh tap water for its products; do not substitute generic ultrasonic-humidifier advice for your model’s 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 Yokohama?
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 Yokohama?
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 Yokohama?
Almost certainly not. Soft water does not usually justify a softener.
Is hard water in Yokohama 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 (Yokohama City Waterworks Bureau: Water Quality Test Annual Report, fiscal 2025 (vol. 76)) 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
Yokohama City Waterworks Bureau: Water Quality Test Annual Report, fiscal 2025 (vol. 76), checked 2026-10-31. Guidance is general; your appliance manual takes priority.
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