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In nature, lime occurs mainly as a mineral rock, but it dissolves easily in water and gives it a certain hardness. This property, which is equivalent to the amount of dissolved calcium and magnesium in water, is expressed in ppm (or mg/L) of calcium carbonate or in French degrees (symbol °f or °TH), which are mainly used in Switzerland and France.
Value range of the hydrometric titer (TH)
|Water (°f)||0 to 7||7 to 15||15 to 30||30 to 40||+40|
|Water||very soft||soft||rather hard||hard||very hard|
Comparison between different foreign and French units
|French degree||English degree||German degree||American degree||Milliequivalence|
Very often, we only remember the inconveniences caused by too hard water (calcified household appliances, rough laundry, etc.). But the more calcareous water is, the richer it is in calcium and magnesium, which are essential for our health. To understand its benefits for the water we drink, the following explains where limescale comes from and how it forms in water, making its way to our taps.
How is lime created?
Limestone can form:
- Either by accumulation of skeletal fragments or calcareous shells, e.g. of corals, mussels or protozoa: Then one speaks of limestone of organic origin,
- or by chemical or biochemical precipitation of calcium carbonate: then we speak of limestone of chemical origin.
Limestone is easily recognised by its white colouring and leaves a kind of powder on the hands when touched. In Switzerland, it is found mainly in the regions of the Jura arc.
The lime content of water depends on the nature of the soil through which it flows from the source to the tap.
How does limescale get into our taps?
Before the water reaches our taps, it passes through a long path in the form of recurring cycles. It passes through different types of soil (groundwater fed by percolating rainwater) and is naturally enriched with the mineral salts and trace elements phosphorus, calcium and magnesium, which are important for our health.
Depending on the geological composition of the soils traversed, the physico-chemical composition of the water is not the same. For example, water that flows through calcareous or chalky soil yields water with a high lime content, while water that flows through crystalline soil such as sand or granite is considered soft.
The water then passes through a drinking water treatment system before it reaches our taps. It retains its natural mineral properties but undergoes various treatments to ensure that it can be drunk without risk to human health.
Limescale is found in tap water, but is also present in bottled water. The hardness of the water has no effect on human health, but very hard water can cause irritation to sensitive skin.
What is the difference between limescale and scale?
- Limescale corresponds to the calcium and magnesium contained in water.
- Scale are deposits that solidify when water is heated: They can be white streaks on drying dishes or whitish deposits at the bottom of a kettle, in pipes, radiators, etc.
How can you protect your household appliances against scale?
- Remember to use demineralised water, which contains no minerals and thus prevents the formation of limescale deposits and also protects your textiles from possible stains.
- Find out about the water hardness where you live. Water hardness depends on the geology of the soil through which the water has flowed, varies from region to region and is proportional to its calcium and magnesium content. It does not depend on its potability. It is calculated in "French degrees" (°f). A water is considered hard if its hydrometric value (TH) is above 15°f. Conversely, water with a TH value below 15°f is called soft water.