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Engineering ToolBox > Soft and Hard Water
"Hard water" is water containing a quantity of dissolved minerals. When hard water is heated, the carbonates precipitate out of solution, forming scale on the heat surfaces.
Soap is less effective in hard water because its reacts to form the calcium or magnesium salt of the organic acid of the soap.
"Soft water" is treated water where the only cation, the positively charged ion, is sodium.
| Dissolved Calcium and Magnesium | ||
| Water | Milligrams per Liter (mg/l) | Grains per Gallon (gpg) |
| Soft | 0 - 60 | 0 - 3.5 |
| Moderate | 61 - 120 | 3.5 - 7 |
| Hard | 121 - 180 | 7 - 10.5 |
| Very Hard | > 180 | > 10.5 |
Hard water can be softened by passing it over an ion exchange resin.