Calcium

The main driver of water "hardness."

What it is

Calcium is the most abundant cation in many hot springs and the main contributor to water hardness. It enters groundwater as it dissolves limestone and other carbonate rocks.

In hot springs

Calcium concentrations vary widely, from a few mg/L in silica-rich acidic springs to over 300 mg/L in hard-water springs. High-calcium water is "hard" and can leave skin feeling filmy.

Cited benefits and context

Research on bathing-water mineral composition and skin is active but mixed. A 2025 study found that the effects of water bathing on atopic dermatitis are determined in part by the water's mineral composition, including calcium and magnesium (Effects of Water Bathing on Atopic Dermatitis, Wiley 2025).

Epidemiological studies have long associated hard (calcium-rich) water with irritation of atopic skin, though dermal absorption of calcium during a short soak is limited. There is no robust clinical consensus that soaking in calcium-rich water treats any skin condition. The evidence is suggestive, not conclusive.

Cautions

Hard water can leave skin feeling dry or filmy. Moisturize after soaking. Calcium in soaking water is not a treatment for calcium deficiency or osteoporosis.

Springs ranked by most calcium

181 springs with verified calcium data · showing top 50 · source: USGS Water Quality Portal

  1. 1

    Alpine Warm Spring

    id · 85°F · primitive

    560 mg/L

  2. 2

    Heise Hot Springs

    id · 102°F · developed

    430 mg/L

  3. 3

    Big Spring

    id · 85°F · primitive

    410 mg/L

  4. 4

    Hot Springs State Park

    wy · 104°F · primitive

    310 mg/L

  5. 5

    Deer Hot Springs

    id · 102°F · primitive

    300 mg/L

  6. 6

    The Landusky Plunge

    mt · 77°F · primitive

    260 mg/L

  7. 7

    Squaw Hot Springs

    id · 102°F · primitive

    250 mg/L

  8. 8

    Malad Warm Spring

    id · 90°F · primitive

    240 mg/L

  9. 9

    Bear Lake Hot Springs

    id · 102°F · developed

    210 mg/L

  10. 10

    Alkali Flats Warm Spring

    id · 85°F · primitive

    210 mg/L

  11. 11

    Bald Mountain Hot Springs

    id · 115°F · primitive

    203 mg/L

  12. 12

    Cleveland Hot Springs

    id · 102°F · primitive

    183 mg/L

  13. 13

    Battle Creek Hot Springs

    id · 102°F · primitive

    160 mg/L

  14. 14

    Prices Warm Spring

    id · 85°F · primitive

    160 mg/L

  15. 15

    Brockman Creek Hot Spring

    id · 102°F · primitive

    150 mg/L

  16. 16

    Yandell Springs

    id · 102°F · primitive

    150 mg/L

  17. 17

    Mammoth Hot Springs

    wy · 162°F · developed

    139 mg/L

  18. 18

    Pincock (Green Canyon) Hot Springs

    id · 102°F · primitive

    130 mg/L

  19. 19

    Woodruff Hot Spring

    id · 102°F · primitive

    130 mg/L

  20. 20

    Owen Cabin Hot Spring

    id · 102°F · primitive

    123 mg/L

  21. 21

    Lava Hot Springs

    id · 130°F · developed

    120 mg/L

  22. 22

    Yellowstone Hot Springs

    mt · 104°F · resort

    114 mg/L

  23. 23

    Pleasantview Warm Springs

    id · 85°F · primitive

    110 mg/L

  24. 24

    Goldbug Hot Springs

    id · 136°F · primitive

    92 mg/L

  25. 25

    Rockland Warm Springs

    id · 85°F · primitive

    92 mg/L

  26. 26

    Maple Grove Hot Springs

    id · 102°F · primitive

    89 mg/L

  27. 27

    Warm Springs

    id · 85°F · primitive

    83 mg/L

  28. 28

    Broadwater Hot Springs

    mt · 151°F · resort

    77 mg/L

  29. 29

    Indian Springs (Resort)

    id · 102°F · developed

    76 mg/L

  30. 30

    Rock Creek Hot Springs

    mt · 112°F · primitive

    75 mg/L

  31. 31

    Ennis Hot Springs

    mt · 193°F · resort

    69 mg/L

  32. 32

    Little Antelope Flat Warm Spring

    id · 85°F · primitive

    68 mg/L

  33. 33

    Cottonwood Hot Springs

    id · 100°F · developed

    60 mg/L

  34. 34

    Tadpole Warm Spring

    id · 85°F · primitive

    58.70 mg/L

  35. 35

    Marsh Gully Hot Springs

    id · 102°F · primitive

    58 mg/L

  36. 36

    Wild Horse Hot Springs

    mt · 102°F · developed

    56.90 mg/L

  37. 37

    Haileys Hot Springs

    id · 102°F · developed

    54 mg/L

  38. 38

    Lake Walcott Hot Spring

    id · 102°F · primitive

    52.40 mg/L

  39. 39

    BLM Well (Frazier Hot Spring)

    id · 105°F · primitive

    51 mg/L

  40. 40

    Alhambra Hot Springs

    mt · 100°F · resort

    49.60 mg/L

  41. 41

    Taylor Springs

    id · 102°F · primitive

    48 mg/L

  42. 42

    Sullivan Hot Springs

    id · 102°F · primitive

    48 mg/L

  43. 43

    Keithly Warm Spring

    id · 85°F · primitive

    48 mg/L

  44. 44

    Beardsley Hot Springs

    id · 102°F · primitive

    47 mg/L

  45. 45

    Banbury Hot Spring

    id · 102°F · primitive

    44 mg/L

  46. 46

    Grape Creek Warm Spring

    id · 85°F · primitive

    44 mg/L

  47. 47

    Downata Hot Springs

    id · 102°F · developed

    43 mg/L

  48. 48

    White Licks Hot Spring

    id · 102°F · primitive

    39 mg/L

  49. 49

    Pray Hot Springs

    mt · 120°F · developed

    36 mg/L

  50. 50

    Barney Hot Springs

    id · 102°F · primitive

    36 mg/L

Sources

← All minerals