| Although it may not be common knowledge, there | | | | and magnesium sulphates and/or chlorides in the |
| can actually be a difference between the type of | | | | water, which become more soluble as the |
| hard water that is supplied to homes throughout the | | | | temperature rises. Despite the name, the hardness of |
| world - water can have a 'temporary' or 'permanent' | | | | the water can be easily removed using a water |
| hardness. There are also common types of hard | | | | softener, or ion exchange column. |
| water depending on the ion (eg. magnesium or | | | | Hard Water Testing |
| calcium) found in the water, which can cause | | | | If you are on a municipal water system, and would |
| different types of hard water stains and limescale | | | | like to find out the hardness of the water to your |
| formation. | | | | home, the water supplier can tell you the hardness |
| Temporary Hardness | | | | level of the water they deliver. If you have a private |
| Temporary hardness is hardness that can be | | | | water supply, you can have the water tested for |
| removed by boiling or by the addition of lime (calcium | | | | hardness. There are several different scales used to |
| hydroxide). It is caused by a combination of calcium | | | | describe the hardness of water in different contexts. |
| ions and bicarbonate ions in the water. By boiling the | | | | The precise mixture of minerals dissolved in the |
| water, it promotes the formation of carbonate from | | | | water, together with the water's acidity or alkalinity |
| the bicarbonate and will precipitate calcium carbonate | | | | (pH) and temperature will determine the behaviour of |
| (the limescale) out of solution, leaving water that is | | | | the hardness, so single number on a scale does not |
| less hard after it has cooled. | | | | give a full description. Descriptions of hardness |
| When it has been heated, less carbon dioxide is able | | | | correspond roughly with ranges of mineral |
| to dissolve into the water. Since there is not enough | | | | concentrations: |
| carbon dioxide around, the reaction cannot take | | | | Soft: 0 - 20 mg/L as calcium |
| place, and therefore the calcium carbonate will not | | | | Moderately soft: 20 - 40 mg/L as calcium |
| "dissolve" as readily. Instead, the reaction is forced to | | | | Slightly hard: 40 - 60 mg/L as calcium |
| re-establish equilibrium, and the solid calcium carbonate | | | | Moderately hard: 60 - 80 mg/L as calcium |
| is formed. Heating water will remove hardness as | | | | Hard: 80 - 120 mg/L as calcium |
| long as the limescale that precipitates out is removed. | | | | Very Hard: >120 mg/L as calcium |
| After cooling, if enough time passes the water will | | | | As a guide, 60% of the UK and 85% of the US |
| pick up carbon dioxide from the air and the reaction | | | | population live in a hard water area, which can cause |
| will again proceed, allowing the calcium carbonate to | | | | stubborn hard water stains on fixtures and fittings. |
| "redissolve" in the water. | | | | Most water softener companies will be able to supply |
| | | | you with a free water testing kit. Once you've |
| Permanent Hardness | | | | tested your water supply, the hardness of your |
| Permanent hardness is hardness (mineral content) | | | | water will be reported in grains per gallon, milligrams |
| that cannot be removed by boiling. When this is the | | | | per liter (mg/l) or parts per million (ppm). One grain of |
| case, it is usually caused by the presence of calcium | | | | hardness equals 17.1 mg/l or ppm of hardness. |