What is limescale in water?
In general language, carbon-related hardness contained in water is also called limescale and designates the share of calcium and magnesium compounds with carbonic acid. Calcium is one of the most frequently occurring elements on earth and exists in almost every type of soil or rock and is vital for organisms. It is a key feature in limestone. Due to its chemical properties, under certain circumstances calcium easily dissolves from existing compounds. As quickly as this occurs, however, it also enters into new relationships. The medium for this constant change is water, which can absorb a certain quantity of unbound calcium.
How does calcium get into water?
Precipitation water constantly absorbs CO2 from the atmosphere which then re-occurs in the ground water, fresh water or ocean water in the form of carbonic acid (dissolved carbon dioxide). This carbonic acid contained in rain water affects the lime contained in rock or soil primarily as calcium carbonate (CaCO3) and dissolves the calcium from within it. Over several thousands of years, water can eat away the limestone meters deep down, hollowing out cave systems and in this way absorbing calcium. Water absorbs calcium only until a balance with carbonic acid is achieved.
How is lime dissolved from water again?
If water in which lime and carbonic acid are in balance is heated or slightly pressurized, gaseous carbon dioxide escapes. Suddenly too much lime is contained in the water and all of a sudden the solution becomes supersaturated. Through the loss of carbon dioxide, part of the calcium carbonate again escapes – in order to restore the water balance.
Where specifically does lime escape from water?
Heating rods in washing machines are real lime catchers. Through the high temperature of the water, CO2 disspiates in the washing machine heating system so that limescale deposits build up here. The same reaction occurs in water heaters and coffee machines.
Hardness ranges 
Three hardness ranges are distinguished:
| Hardness range I |
to 8,4°dH (soft water) |
| Hardness range II |
8,4 to 14°dH (medium soft water) |
| Hardness rangeIII |
more than 14°dH (hard water) |
How does a conventional table-top water filter change the overall hardness of water?
When determining the overall hardness, the sum of calcium and magnesium ions is measured; both together form the total hardness level of water. With conventional table-top water filters, calcium and magnesium are removed from the water and exchanged against H+ and potassium; the total hardness therefore decreases. We then talk about ‘soft’ water (provable e.g. with a test strip). The disadvantage: Not only lime, but also the physiologically valuable mineral magnesium are removed from the water. How this can be avoided is detailed here: > Hardness degree in drinking water