There water hardness indicates the amount of calcium and magnesium ions contained in it. It is measured in millimoles per liter (mmol / l), but more often it is expressed in German degrees (° dH) or in French degrees (° T.H.). The respective reference scales are as follows: fresh water ° dH 0-7 / T.H. 0-15; hard water ° dH 8-14 / T.H. 16-25; very hard water ° dH> 21 / T.H.> 37.
In 'domestic practice' the water hardness it is equivalent to limescale deposits that form in pipes (especially in metal ones, less so in plastic ones) in sinks and on taps: the harder the water, the more evident the problem is. With a simple kit for measuring the quality of water that you find in pharmacies or online, you can check the extent yourself.
Fortunately, hard water is harmless to human health (if this were not the case we would have a serious problem) even though it is not for household appliances, which have serious problems with limescale deposits. Plants also suffer from water hardness and watering can become a dilemma.
How to correct the hardness of the water?
The simplest method to 'soften' the water a little in case of temporary hardness is to boil it, an operation that precipitates at least the insoluble calcium carbonate. However, knowing it doesn't help us much, also because the chloride salts and sulphates are co-responsible for water hardness (permanent hardness) do not change in boiling. More useful is knowing that the water hardness it can be corrected by adding a little soda (if we are talking about cleaning water) or sodium bicarbonate (if we are talking about drinking water).
If that's not enough, there are filters and softeners. With the former, it is possible to retain solid particles, while providing for accurate installation and maintenance. Softeners, on the other hand, use a chemical process based on the use of a resin charged with sodium ions (salt) to capture and precipitate (in the drain) the metal ions. The resin must be refilled from time to time, usually with normal table salt.
Many ion exchange water softeners do not need to be connected to the electrical network because they work mechanically by exploiting the water pressure. Even the regeneration of the resins is automated in many devices and it is sufficient to top up with salt from time to time. There are various sizes and the sizing depends on the amount of water used (which usually varies according to the people).
Then there are the electromagnetic water softeners, which work differently and the result is also different. For these you need an electrical connection but the installation is external to the water pipe and no chemical refills are required. The difference in the result is that, while ion exchange softeners modify the chemical structure of water (sometimes making it too rich in salt, attention!), Electromagnetic ones simply break down the limescale favoring its elimination as the water flows. . In the industrial field, where water flows continuously in large quantities, they are considered very effective, at home perhaps a little less. On the other hand, there is no problem with salt, maintenance and they don't cost much.
If you want to measure the quality of the water in your home (hardness, but also pH, sulphates, nitrates ...) I recommend the Bicocca University of Milan kit that you can buy online (less than 20 euros). Is called Immediatest
If you want to experiment with an electromagnetic softener you can try this water softener
For ion exchange softeners, if you are not very familiar with plumbing and do-it-yourself, my advice is to contact an expert for installation.