[nephanth]

It's not even hard, just boil a solution of 1/2 white vinegar + 1/2 water, and the CaCO3 (+ 2H(+) from the vinegar) changes back to Ca(2+) + CO2 + H2O You can even see the bubbles from the CO2

[Adverblessly]

I'd recommend using citric acid instead, they sell it here as "lemon salt" so it comes in an easy to use salt shaker. I usually put it in the minimum amount of water required to safely boil it and a small amount depending on how heavy the deposits are (usually up to a spoon is enough for me), though you could also just pour it in and wait.

It works really well and doesn't leave the same smell. When I'd previously used vinegar I'd had to boil another round of water and throw it away just to clean the kettle from the vinegar itself, but with citric acid there's no need (just don't drink the citric acid, it tastes like acid :)).

[badtension]

Do you recommend citric acid over vinegar just because of the smell?

I use vinegar all the time, put in something like 50 ml to the remaining hot water just after making a tea. After a few minutes you can just rinse it and let it evaporate, 5 more mins and the smell is totally gone.

[Moru]

It's pretty inconvenient when you are in an unknown location on a hotel. But yes, some areas of Europe has very hard water.

[eru]

For making coffee or tea, soft water is preferable.

For drinking straight up, hard water tastes better. At least to me. Perhaps because that's what I grew up with in central Europe.

Btw, the Romans also built their towns preferably in places with hard water.

[Moru]

I come from a soft water area and I prefer the soft water for drinking. Our water cooker never needs vinegar, it's just not getting the residue :-)