June 11th, 2008

Reboiling Points
Boiling Water Multiple Times Not As Harmful to Health As Thought

There was an elderly tea lady (let’s call her Mrs D) at the place I used to work. She wasn’t a tea lady in the traditional sense who’d wheel her trolley of goodies at teatime — she prepared refreshments for our weekly meetings — but she loved observing me while I brew a cuppa in the office pantry, which made me slightly nervous at times.

I was about to make myself a cup of instant coffee one day when I found the electric kettle filled with enough water to make a warm cup of coffee. Because of the ridiculous subarctic temperature of the office, I preferred my coffee tongue-scalding hot so I did what I thought was the obvious thing to do — I turned the kettle back on.

Shocked Tea lady Already anxious by her mere presence, I was startled silly when Mrs D boomed, “What on earth are you doing?! Why are you boiling the water again? You’re not supposed to do that!”

I told her about my coffee temperature preference but she continued disapprovingly, “but you’re not supposed to reheat water that’s already been boiled!!!” When I tried asking her the reason why she kept saying that I wasn’t supposed to. I asked another colleague who happened to be there and she said the same thing, “you’re not supposed to boil water multiple times because it’s not good for you!!!”

Outnumbered with no desire to argue, I left the scene with a less-than-hot cup of coffee.

Being the naturally curious person that I am, I decided to ask the rest of my colleagues about this. The consensus was nearly unanimous(a few had never heard of it) — you shouldn’t boil water more than once — the reasons were similar – reboiled water is not good. Why exactly? They didn’t have an answer.

I wasn’t convinced and brushed it all aside as old wives’ tales. However, despite my numerous make-coffee-while-no-one-is-around attempts later, I kept forgetting to research the reasons and origins for this theory.

Coffee Beans

5 years later

I was at a coffee house while waiting for my camera to be serviced the other day when out of boredom, I decided to read all their coffee and tea leaflets. There was a section devoted to the importance of using fresh water for brewing coffee and tea. I didn’t think much about it until much later when I was making meyself a cup of coffee at home.

Remembering the Water Mystery from half a decade ago, I consulted my friend Google: Reboiled water causes cancer? - not true unless your water is already toxic to begin with. Reboiling causes water to harden? - not true either. Then I found this:

10 Tips for A Better Cup of TeaTea Leaf

The more oxygen that is dissolved in water, the better it tastes. So, to make sure you use water with the maximum amount of oxygen, don’t re-boil any leftover water in your kettle. Water that is boiled too much becomes poorly aerated because oxygen atoms escape in the form of steam. By always filling your kettle up afresh, you are ensured fully aerated and tasty water.”

Ten Tips for a Betta Cuppa-Fresh Water, Best water MSN Encarta

Mystery solved.


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Comments: 7 Comments | Add your comment
Fascinating. I've never heard that there was anything wrong with reboiling water, although I know enough chemistry to know that water is water and heating it doesn't change that, unless you get it hot enough to start splitting the molecules. As an aside, I love the Britishism "cuppa". It always reminds me of that lovely Kinks song "Have A Cuppa Tea". Unfortunately I can't use it myself because my fellow Yanks look at me strangely when I do.
Christopher Waldrop  at 10:36 am on June 11, 2008
I reboil water all the time :) But then, I prefer coffee to tea so I've managed to miss all the many "rules" related to tea making, such as when the milk should be added, what type of cup is best to use etc!
Mags | Woo-Woo Wisdom  at 2:26 am on June 12, 2008
Mags, always add the milk first. It prevents scalding. There used to be a place down the street from my office that served afternoon tea. I miss it, especially since I never had to worry about things like reboiling the water.
Christopher Waldrop  at 8:20 am on June 12, 2008
Although I drink a lot of coffee and tea, I've never been a connoisseur, so I don't know much about the art coffee/tea making so thank you for the additional info Christopher.
I love the idea of a leisurely afternoon tea but at the moment I don't even have enough time for to properly enjoy my short coffee breaks!
Ginger M  at 11:31 am on June 12, 2008
Until recently I didn't know the scientific base behind a so-called 're-boil' taboo either, but then again I just didn't like the taste of re-boiled water. It tasted sort of stale. Thanks for the article! Love your site, by the way!
Anya  at 1:23 am on June 13, 2008
Oxygen makes it taste better?! Riiight. So thats what my brocolli soup is missing....air!!
Colin  at 8:45 am on August 31, 2008
Steam escaping from the water doesn't make it harder. 2H2+O2 2H2O + energy (I think) Thus oxygen escapes and the hydrogen molecules also escape. You're not going to have a kettle filled with Hydrogen if you boil it long enough, the water is just getting less as it escapes into the atmosphere. Water is water. If you remove the oxygen you'll be drinking hydrogen.
Wicus Lab  at 1:40 am on September 10, 2008

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