* Hardness is caused by dissolved minerals: Hardness in water is primarily caused by dissolved calcium and magnesium ions. Boiling water doesn't remove these minerals.

* Boiling only evaporates water: When water boils, the water molecules turn into steam and escape, leaving the dissolved minerals behind.

* Some minerals may precipitate: In rare cases, some minerals like calcium carbonate (CaCO3) can precipitate out of solution as the water boils. However, this usually occurs only in water with very high hardness levels, and the amount of precipitate is often minimal.

Here's what boiling water does:

* Reduces dissolved gases: Boiling water removes dissolved gases like oxygen and carbon dioxide, which can affect taste and odor.

* Kills bacteria: Boiling water at a rolling boil for 1 minute kills most harmful bacteria.

To soften hard water, you need to use other methods:

* Water softeners: These systems use ion exchange to replace calcium and magnesium ions with sodium ions.

* Reverse osmosis: This method forces water through a semipermeable membrane, removing most impurities, including hardness minerals.

* Lime softening: This method adds lime to precipitate out calcium and magnesium as calcium carbonate.

In summary, boiling water does not change its hardness significantly. It simply concentrates the dissolved minerals as the water evaporates.