Is Twice Boiled Water Bad For You? The Answer Might Shock You!

Is It Safe to Reboil WaterBoiling the same water twice won't likely kill you (slowly or otherwise). At worst, it might make your tea slightly less palatable.

You may have heard that “reboiling” water is potentially harmful to your health, and that regularly doing so increases your chances of getting cancer. tries to show the general reasoning behind why this happens on their website:

“When we boil water, the chemistry of it changes, which is usually a good thing as it boils out volatile compounds and dissolves gases. This is why boiling water mostly ensures that it’s safe to drink. If water is left to boil for too long or is revealed, the chemical compounds change for the worst. By leaving your water to boil down, you are actually concentrating many harmful chemicals instead of getting rid of them. The same thing happens when you reboil water, as the compounds concentrate and increase the risk of ingesting certain chemicals”

The above website also goes on to suggest that reboiling water will expose you to toxic amounts of things like arsenic, fluoride, nitrates, and even includes the words “reboiled water causes cancer” right in one of its URL’s.

Countless others agree, posting that consuming reboiled water is akin to drinking filthy bilge water filtered through a hobo’s socks that have been previously stored at ground zero at Chernobyl.

So with all this anti-reboiling water found online is it really true that drinking reboiled water is bad for you? No, not at all.

While the kind of water that pours from our faucets does contain innumerable impurities, some of which are, at least from a practical standpoint for most home consumers, impossible to filter out entirely, such as nitrates.

Science tells us, the concentration of these impurities are not generally harmful in the normally negligible quantities you’d find in your common tap water.

But, what about the claim of boiling down that water and concentrating all those harmful impurities?

When some of the water evaporates as the water boils, while some of the impurities are removed, others remain (called non-volatile substances) and are now more concentrated than when the volume of liquid was greater. This is absolutely true. But it’s still not bad for you.

Here is why.

Let’s say you are boiling a pot of water for some tea. You pour a cup, then over the next few days you reboil the water every time you want another cup. While, it’s true that each time you boil that pot for another cup, the impurities will be concentrated. Still, you’d wouldn’t be able to have more impurities than you would have in just drinking the full pot of tea to begin with.

Generally, boiling water, allowing it to cool and then reboiling it does not present much of a health risk. You aren’t likely to endanger your health by doing so. Also, keep in mind not one single public health agency in the world advises against drinking twice boiled water.

So unless you have some kind of troubled drinking water in the first place or boiling down water in some extreme unrealistic scenario, reboiling your water is perfectly safe.

Fun Fact: If you have perfectly pure distilled deionized water, nothing will happen if you reboil it.

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