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.

Edit: Thanks to the comment by Mihai, I suddenly remembered learning about water aeration in school. Here’s a bit more on that:

Aerated water is, correctly speaking, distilled water to which purified air is added to improve its flavor. Wikipedia”

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Comments: 25 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
Even I have heard that reheating the water and drinking such water is equal to poison.I am writing in my blog and when searched the net for reasons I saw ur blog and for accurate reason I am unable to find it on net. :)
bhuvaneswari  at 4:29 am on November 18, 2008
look for "Dissolved oxygen" on google. Water molecules don't break in H2 and O, it is simpler to understand if you think of fish in an acquarium. Regarding making tea, it would be better to do it with freesing water, or at least not to boil it. Hope this helps.
Mihai  at 6:01 am on January 8, 2009
My wife didn't want me to buy an airpot. So, she said that re-boiling water is not good for health. My mother-in-law similarly said she heard this over the radio. Now, I'm convinced that it is indeed an old wives' tale possibly from England who are particular about their "Cuppa"!!
Shang  at 6:42 am on February 19, 2009
water is h2o right? if the oxygen is detach, then the rest is just hydrogen.. so its 1 water molecule less.. the rest of the water is still h2o.. so i dont get it, why oxygen escape? why not hydrogen escape, giving us more oxygenated water?
hweegan  at 8:44 pm on March 24, 2009
Oxygen that gets removed from boiling is not from the water molecules i.e not taking O2 out of the H2O. It is the oxygen that is dissolved in the water. The air dissolved in water is why you see bubbles when you are boiling water. And also why fish and other aquatic organisms can actually live in water. They too need oxygen to breathe and live.
Siew  at 2:53 am on April 3, 2009
Water contains dissolved oxygen approx at 8 ppm (parts per million concentration), depending on temperature. Water, after being boiled, is NOT void of oxygen. Oxygen would simply redissolve into it. Look up a oxygen solubility chart (conc vs temp) for more info.
Stan  at 8:41 am on July 12, 2009
The issue is not really the dissolved oxygen. Think where the water that you boil comes from. Is it distilled H2O? not very likely. Therefore, it will have components other than just H2O, typically a variety of dissolved minerals. That's natural and nothing to worry about. Of course, humans and their chemistry and their impatience do many 'unnatural' things to the environment: chemicals for us, for our animals and plants, transporting water through less-than-ideal pipelines, etc. Certain of these chemicals can enter our water supply and remain in significant concentrations in the water. Normally, these chemicals (such as nitrates) may be below toxic levels. But what can happen during boiling is the chemicals are concentrated. First, just the act of boiling concentrates the chemicals, since a certain percentage of the water evaporates in the process. Obviously, if one reboils the water, they will continue to concentrate the chemicals even further. Second, imagine you have a small amount of boiled water in the kettle (hence, increased concentration of the chemical) and you fill it up (without first emptying). Now you have actually increased the concentration of chemicals in the kettle above that of the normal tap water. If you repeat this procedure, the concentration can get quite high. Of course, all this depends on where you live and what your quality of water is, so it's not a general rule. I find it interesting that, after living in 3 other countries, I only encountered this issue when I came to England. Anyway, if you do occasionally reboil it's not likely to kill you, however, I would suggest you at least empty the kettle into the sink before refilling it.
Edwin  at 8:00 pm on December 3, 2009
The note about not reboiling water because it loses oxygen is incorrect. If you think about it a little, isn't boiling the water the first time going to lose the oxygen as steam? Why does boiling it again make a difference? One counterargument may say that reboiling will cause more oxygen to leave, but that is not true If you have taken chemistry in high school, you may have learned about solubility. Gases dissolve in water, and a gas is more soluble in cold liquids (hence why warm soda is flatter and easier to explode, because the gas escapes). When you boil water to 100C, the solubility of oxygen at that temperature decreases, and thus there is not as much oxygen in the water (also, it does not lose it in/as steam). However, once you stop boiling the water, the solubility increases (because its getting colder). If you boil it again, the solubility will drop again, but only to the point it normally does when it is at 100C. So the concentration of oxygen never gets below whatever it is at 100C, regardless of the number of times boiling If you want more aerated water, then its not the number of times you boil it, but the temperature you boil the water to. Water boiled to 80C will have more oxygen than water at 100C
Stan  at 9:35 pm on February 8, 2010
[...] reboiling water doesn’t make the best cup of tea according to the top ten tips for making a cup of tea: The more oxygen that is dissolved in water, the better it tastes. So, to make sure you use water [...]
Twitter; Twettle « Mike Street Media – Freelance Website Designer  at 7:56 am on April 22, 2010
how bout boiled water to make milk for infants and children? Since oxygen content of water will decrease if boiled more than once.Logically it still doesn't change my mind about this and i just argued a little with my sister about this . hahaa :)
mike  at 9:46 am on June 23, 2010
Yes re-boiling water does make it hard. The minerals in the water obviously aren't being boiled off into the atmosphere. They either stay in the water or become "scum" on the side of the pot/pan. Try this test... Boil a few cups of water in a pan until a small amount is left, and see the buildup on the sides of the pan... that's the minerals from the water. You could go so far as continuing by adding more water without cleaning the pan and continue to boil a few times then swirl the water around the pan and take a taste of the water... It's going to a "harder" more mineral rich taste to the water. Namaste
Mr. tea  at 5:23 pm on September 9, 2010
wicus lab and Hweegan, Do you remember nothing from science class? (or are you Americans?) Read Siew's comment. We're talking about 'Dissolved Oxygen', not the Oxygen component of H2O.
B.f.B  at 7:04 am on December 21, 2010
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Theewater: vaker koken?  at 8:01 am on February 22, 2011
actually in food science there is already studies and confirmation that the air particles inside water actually makes the water or soup or whatever liquid tastes better. its got to do with the oxygen molecules breaking down the molecules that produces the different tastes into smaller molecules so that your taste buds can taste it better. thats why adding alot of oxygen into soups makes it taste even more refreshing. for example, bottled ice teas, open one up and drink a mouthful, remembering to taste the tea and the sensations on your tounge. then shake the bottle vigourously until it is full of foam on the top. then take another sip and compare the difference. oh, try and close your eyes as you drink it, it makes the taste stand out even more.
J  at 5:44 pm on May 25, 2011
It is a hint after sterilizing water by boiling to pour it back and forth between two pots to improve the taste. This is the only reason. Personally, I don't think that oxygen, which is a gas, will hang around long in 200 + degree water.
El Gato  at 12:01 am on December 13, 2011
Evidence comtradicts your claim, as upon the first boil water is left devoid of oxygen http://www.engineeringtoolbox.com/air-solubility-water-d_639.html
Conor Graham  at 6:01 pm on March 20, 2012
[...] an article on GrowingHappiness.com about reboiling water: The more oxygen that is dissolved in water, the better it tastes. So, to [...]
Better Oxygen = Better Taste = Better For You | | OxygenSuperCharger.com BlogOxygenSuperCharger.com Blog  at 8:02 am on April 23, 2012
@Christopher Waldrop add the milk first,it avoids scalding!! scalding what exactly?the tea is already brewed and off the boil if its been allowed to brew,addind milk before or after makes no difference,if your thinking the temp drops too much if you add the tea first all you have to do is scald the cup first
Stuart  at 10:44 pm on August 31, 2012

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