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Water Hardness
Hardness from CaCO3 in degrees of hardness, parts per million and
milligrams per liter
| Hardness |
‘dH |
ppm |
mg/L CaCO3 |
| Soft |
0 - 4 |
0 - 70 |
0 - 75 |
| Slightly Hard |
4 - 8 |
70 - 140 |
75 - 150 |
| Moderately Hard |
8 - 12 |
140 - 120 |
150 - 225 |
| Hard |
12 - 18 |
210 - 320 |
225 - 340 |
| Very Hard |
18 - 30 |
> 320 |
> 340 |
1‘dH = 17.8 ppm = 17.9 mg/L
Hardness of water for Mg and Ca ions in
grains per US gallon and milligrams per liter
| Hardness |
gpg |
mg/L CaCO3 |
| Soft |
0 - 1 |
0 - 17 |
| Slightly Hard |
1 - 3.5 |
17 - 51 |
| Moderately Hard |
3.5 - 7 |
51 - 120 |
| Hard |
7 - 10.5 |
120 - 180 |
| Very Hard |
1 > 10.5 |
> 180 |
1gpg = 17.1 mg/L
Many different scales of hardness are used, and
the conversions are not well defined. This is a rough scale
equating the various definitions of hardness.
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