This is the reason why you should never boil the same water twice!
Are you emptying your kettle every time after you boiled water?
Or maybe you made hard eggs and don't want to waste the remaining water.. so what do you do with them?
Usually you probably don't empty the water right away, they just sit there in the kettle until the next time you boil them.
Sounds harmless, doesn't it? well no! The opposite is true.
Let's take a closer look at what happens when we boil water. At first glance, you see little bubbles and steam, but something else happens at the chemical level. By boiling them several times, the oxygen content changes and hazardous substances begin to accumulate.
One can feel the difference in taste when making tea: the taste of fresh water tea will be quite different than tea with water that were boiled again.
Boiling water is a great way to kill bacteria definitely, but when you boil water over and over again, dangerous gases and toxic substances like Arsen, Nitrate and Fluoride can form as a result of changing the chemical structure. Many studies have shown the connection between fluoride and the harmful effect it has on the nervous system and brain.
So after all this, you're not only drinking water, and the minerals that are actually good for you, like calcium, can cause problems such as kidney stones.
So that's why you should not boil water twice. Of course, the damage is caused when the water is consumed in large quantities.
A small amount is unlikely to cause serious problems, but you may want to give the remaining water in the kettle to your plants instead - it is not harmful to them at all.
So you should definitely be careful and know the consequences when you boil the same water regularly.