Is it safe to boil water multiple times?

Turning on the kettle for a nice cup of tea; it’s something everybody does. It won’t be the first time (and certainly not the last) that we forget we turned on the kettle. When we get back to it half an hour or even an hour later, the water won’t exactly be warm anymore. That’s when we simply turn the kettle back on and wait for the water to boil a second time, so we can finally enjoy our cup of tea. This sounds very innocent, but is it really?

We regularly get questions about boiling water. Some sources say that it’s not good for you to boil the same water more than once. But is this really true? Plenty of reason for us to take a good look at the topic.

Reboiling water

A lot of articles on reboiling will say the following: when you reboil water, dangerous components will gather in the water instead of escape from it like it does normally. The following harmful substances are said to be found in reboiled water: arsenic, nitrates and fluoride. Would you buy a bottle of water that says “contains arsenic” on the label? Of course not! So why would you reboil water if you think there’s a chance it might contain arsenic afterwards? Healthy minerals will continue to exist in boiled water, but they could become dangerous when you reboil it several times. Calcium salts could gather in the water and cause gallstones and kidney stones.

That’s what some of the articles say. But is there any truth to this?

Urban myth

To get to the point right away: reboiling drinking water is not dangerous. So, what’s the deal with this? It’s indeed possible for harmful substances to amass in water if it’s boiled several times. The drinking water we consume does indeed contain arsenic, nitrates and fluoride, but in such small quantities that it cannot lead to health risks if it’s boiled more than two times.

Dangerous

It only gets dangerous to consume reboiled water when 10,000 litres of water gets boiled down into only one cup of coffee or tea. Which is something nobody ever does, of course. So, the next time you’ve boiled some water and forgotten about it, don’t hesitate to simply reboil it. You can safely drink that cup of tea – it won’t do you any harm.