Water hardness / San Jose
Is San Jose water hard? In many areas, yes.
In many areas, yes. San Jose tap water measures 77 to 440 mg/L of hardness as calcium carbonate, which is moderately hard to very hard on the USGS scale. It is the range San Jose Water publishes in its San Jose Water Hard & Soft Water FAQs, which gives no average. San Jose Water publishes separate ranges by supplied source type. Use its supply map for the predominant source at an address.
Where San Jose sits on the scale.
San Jose's published range is 77 to 440 mg/L. On the USGS scale, that is moderately hard to very hard.
0–60Moderate
61–120Hard
121–180Very hard
180+
What it means for curly hair
Calcium and magnesium from hard water settle on the hair. Lab work shows hair takes up a limited amount of these minerals, and damaged or bleached hair takes up more than healthy hair (Evans, Marsh and Wickett, 2011).
The evidence on breakage is mixed: two small studies found lower strength after repeated hard-water rinses (Luqman et al., 2016 and 2018), while an earlier one found no clear difference (Srinivasan et al., 2013). So hard water is a likely factor, not a proven cause.
Hard water is a plausible factor, not a proven cause of breakage. Sudden shedding, itching, flaking or scalp pain needs a dermatologist, not a chelating routine.
Change less. Learn more.
What to try
A city number is context, not a diagnosis. If a change began after a new water source, compare one wash with a product labelled for mineral deposits and keep the rest of your routine the same.
Change one thing at a time and compare the next two or three wash days. The effect of a specific formula is not guaranteed.
If your hair is bleached or color-treated, go slowly and stop if the experiment leaves it feeling less manageable.
What to avoid
Do not turn one experiment into a fixed routine without a consistent reason to keep it.
Do not blame the water for sudden shedding, itching, flaking or scalp pain. That is a reason to see a dermatologist.
Every number keeps its source.
Hardness as CaCO3 by source type: imported surface water 77–153 mg/L; mountain surface water 84–198; groundwater 183–440.. Classified with the US Geological Survey bands (soft 0 to 60, moderately hard 61 to 120, hard 121 to 180, very hard above 180 mg/L). Period: current official guidance. Checked against the source on 2026-10-20. Rizzado did not measure this water.
The San Jose Water report is public: San Jose Water Hard & Soft Water FAQs. Hardness can vary by area and season, and private wells or buildings with their own treatment can differ. If you want your exact value, ask the utility for your address.
Sources
- San Jose Water Hard & Soft Water FAQs
- Evans, A. O., Marsh, J. M., Wickett, R. R. (2011). The uptake of water hardness metals by human hair. Journal of Cosmetic Science, 62(4), 383-391.
- Luqman, M. W. et al. (2016). Effect of topical application of hard water in weakening of hair in men. Journal of the Pakistan Medical Association, 66(9), 1132-1136.
- Luqman, M. W. et al. (2018). To evaluate and compare changes in baseline strength of hairs after treating them with deionized water and hard water. International Journal of Trichology, 10(3), 113-117.
- Srinivasan, G., Srinivas, C. R., Mathew, A. C., Duraiswami, D. (2013). Effects of hard water on hair. International Journal of Trichology.
- U.S. Geological Survey. Hardness of water.
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Your water is one part of the picture.
Rizzado uses your city's water hardness, when there is a primary source, to adjust your routine. If your city is not here, it treats the value as unknown.
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