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A word on the side

It’s been a long long time since I wrote something here and I kind of already filed off this experiment as an idea that didn’t really fly, but I have been writing so many geeky postings on FB lately that I did decide to relaunch this one and see if I still feel like continuing.

Anyhow what triggered this was the amount of nerdy, sciency discussions that I have been leading of late – concerning science stuff, theories or surprising absence of factism – and I spent so much time looking up stuff that I thought I might as well put the information somewhere, since I have made the effort.

Also, I decided to link this to FB, since this was where I was having most of the discussions, and it has been an open discussion anyhow if I place my assorted ramblings there, for that’s probably the network that I have spent most time on…

So now, coming to what brought me to writing today.

A friend of mine had been stumbling over an article of the „aluminium hat“ category. So, an item where people are afraid of something that seems to be fairly standard, because of a seemingly sciency factoid that turns something simple into something lethal.



Aluminium hats and reboilt water

In this case – boiling water that has been boilt before.

The origin of it was a german article – for those of you who read german – that was sent to me by a friend of mine.

It is linked to an article in english, which – no surprise – is on a site that sells water softeners and filters.

Let’s start with recalling the key points of this genius line of argument:

  1. Reboiled water loses its oxygen content through evaporating dissolved oxygen molecules, thus curbing the brewing effect. Therefore reboilt water has less oxygen than boilt water.
  2. Leaving water to sit and then reboiling it can increase the concentration of  certain chemicals such as: arsenic, flouride and nitrates.
  3. The increase in concentration of calcium via reboiling can have a severely damaging effect, leading to: arthritis, gallstones, kidney stones and hardening of arteries.
  4. Leaving water to stand in our kettle, which runs the risk of rusting the metal element. I don’t think any of us need a doctorate to determine that drinking rusty water doesn’t taste nice and isn’t that healthy!

(Of course, the site continues to reassure that if you buy their filters and use them to purify the water, you can reboil it as often as you want…)

Now, let’s continue to look at it in a sort of consolidated manner:


The thing with the oxygen.

Yes, it’s true. Liquid water contains some amount of dissolved oxygen. The usual concentration in natural water is something between 14 mg/l (at 0°) and… well. 0 mg/l obviously, in boiling water.

In natural water, the oxygen content depends on a number of oxygen producing and oxygen destroying processes. The chief ones usually are

  1. saturation value of oxygen in the water: that one says how much oxygen can get into the water at all. It is, almost singularly, depending on temperature (salt content etc being secondary effects). The higher the temperature, the less oxygen there will be in the water. Same, by the way, goes for other gases.
  2. size of the water surface vs its volume: Oxygen enters the water mostly via the atmosphere, therefore the larger the surface is, the larger the area for interaction. And the more oxygen will enter the water.
  3. turbulence of air and water, especially at the surface: Turbulence in air will bring fresh oxygen to the boundary regions to the water surface. Turbulence of water will transport oxygen-rich water to lower regions, transporting water with low oxygen levels to the surface. Also, turbulence improves the surface-to-volume-ratio (see size of water surface)
  4. photosynthesis of water plants: photosynthesis creates oxygen out of light and CO2
  5. breathing of animals and plants: Obvious for animals, but yes, plants also use breathing as an energy source, although during daytime it is vastly overpowered by the process of photosynthesis.

Obviously, when talking about boiled water, I sincerely hope we only have to deal with point 1-3, unless you have a serious contamination in your plumming!

So what happens when you boil the water?

First thing – yep, the article is right. The oxygen leaves the water. The higher the temperature gets, the more oxygen is dispelled, and thus indeed the boilt water has less oxygen than the unboilt one.

Now, that’s bad news, but the good news isn’t far behind.

Once the boiling stops, the water cools, the oxygen seeps back in. It’ll take time, and a bit of stirring (turbulence, you remember?) wouldn’t go amiss, but eventually, you’ll have some oxygen back.

It takes some waiting,though. But within a few hours, you should be ok.

And even if you won’t – there isn’t really that much advantage of oxygen in water.

There is a general myth that oxygen helps release the taste in tea leaves – but, seriously? I mean, we have just established that in boiling water all oxygen is more or less gone from the water, so that doesn’t make that much sense, does it?

I’d worry about the oxygen content of water if I were a fish – there’s really a critical concentration below which fish get into real trouble (one of the reasons why global warming actually in itself can lead to fish death) – but I wouldn’t worry so much about it as a human being. The oxygen is much less in concentration than anything that you breathe in; and on top of it, we all know that we don’t so much like to have too much gas in our digestive organs.

I think you get the picture…

In short, oxygen in drinking water isn’t dangerous, but lack of oxygen in drinking water isn’t really a problem at all. (Otherwise, why recommend hot beverages if you’re feeling bad?)

So, no panic on that front, but let’s move to the next one


Arsenic, fluorites, nitrites – scary stuff

Yeah, that does sound scary. Especially arsenic is really dangerous stuff, and no one would want that in their drinking water, but also the unhealthy aspects of the other two are fairly well documented.

So yes, I wouldn’t want to drink water with a lot of any of those in it, and UNICEF did recognize arsenic in drinking water as a major issue in some areas of the world.

All three (arsenic, fluorite and nitrite compounts) enter the water via the groundwater. In some areas, due to the composition of the layers of the earth crust where the groundwater is assembled, a higher concentration of those is reached, simply because they are water soluble and have been near the soil that contained these materials for a long time. It is actually something quite natural, although, unfortunately, it is also something that’s not too good for mankind.

Now, what about the reboilt water?

First, take a look at the molecule for arsenic acid (which is one of the compounds you’d expect in drinking water):


There’s a lot of H’s and O’s for sure, but in the very center, crucial to the molecule, there is arsenic.

And that’s the point we have to remember. To get arsenic compounds in water, you have to have arsenic. If you want more arsenic compounds, you need to get more arsenic.

So. Where could ‘more arsenic’ come from in boiling – or reboilt – water?

  • either it was in the water to start with. Then we are in the realm of the groundwater considerations as quoted above. Clearly though, reboiling doesn’t put the water near those arsenic soils again – so there should be no additional arsenic atoms that way.
  • Can arsenic be created by boiling? Clearly not. When we boil something non-radioactive under the conditions of reasonable pressure, temperature, etc, what usually would happen, at most, is chemistry. Molecules could form, but to turn one atom into another, that’s not chemistry, that’s nuclear fission or fusion (depending if you go to heavier or less heavy atoms). If you can get that to work in boiling water, thus turning any atom related to water into an arsenic atom – congratulations. You defied the laws of science as we know it today and are probably in for a nobel prize.
  • Can arsenic come from the air? Hopefully not, unless you have some really high arsenic concentration in the air. Even more difficult, given that at room temperature, arsenic is in solid state
  • Can arsenic come from the pot we are boiling stuff in? Hopefully not. Word of advise: Don’t buy a pot that contains an arsenic coating. Or a fluoride coating. Or nitrite coating. If you don’t do that, you should be ok.

So no truth at all to the myth?

As many myths, this one contains a grain of truth as well.

Let’s imagine, we already have arsenic contaminated water. Now, if we start boiling the water, some of it will evaporate. The arsenic acid, however, will not evaporate so easily. So, while the number of arsenic acid molecules will remain constant, the amount of water molecules, in correspondence, will decrease. Therefore, the concentration of arsenic, in total, will increase.

Now, this is not singularly a factor of reboiling water. In fact, that one will happen every time that you have evaporating water, so keeping water boiling for a long time is just as, if not more dangerous than reboiling. This only depends on how much water evaporates – so, all things considered, cooking yourself a nice pot of rice (where the water is constantly kept boiling until it has all been sucked up by the rice) is a much more dangerous thing than reboiling water.

Let’s keep perspective here.

That having been said, it’s good to know (and keep in mind) that there are some areas in the world where arsenic poisoning of water is a real thing. So if you’re in any of those areas, I’d try to get some general information on how to avoid too much arsenic uptake by drinking water.

Too much calcium?

OK, let’s for once get down and run some numbers, shall we?

Let’s say, we have your everyday munich tap water. That’s fairly calcium rich, having 83mg/l of calcium.

The 83mg/l are an average value, the variation is between 72 mg/l and 83mg/l

Now we heat up 1 liter of water (including 83mg of calcium) to 100°C and start boiling. The amount of water that will evaporate is given by m=E/H. E being the energy that is placed into the system, H being the vaporization (so the amount of heat needed to evaporate one mol of a compound). For water at 100°C, that’s 40kJ/mol.

Now we neglect the fact that the water already evaporates below 100°C, and subsequently also neglect that not all the heat energy will be used to evaporate, but some will be used to keep the water on temperature. Let’s say we have an average water boiler that gives 1000W, but since they are not 100% efficient, lets assume 50% efficiency, which leaves us with 500W to evaporate the water.

Say the water boils for a minute (which is already fairly generous using a water boiler)

Then we have m = (500 W*60s)/(40kJ)mol = 30kJ/40kJ mol = 0,75mol

One mol of water is 18 g, so 0,75 mol is 13,5g, equals 13,5 ml.

That means we have lost 13,5/1000=1.35% of water. We now only have 0,9865l of water – but still 83 mg of calcium. Rule of 3 tells us we now have 84,1 mg/l of calcium. That’s still very well within the local and temporal variation of above.

It’s only a rough calculation (quite conservative though), and it doesn’t even consider that some of the calcium will actually remain in your water boiler – as anyone living in Munich can tell you :-).

The natural color of the inside a stainless steel water boiler over here is clearly white.

So. Really, really, once you run the numbers there is no need whatsoever to panic.


Last but not least – the rusting kettle

OK. Let’s make this very short.

I don’t know about underdeveloped countries, if there are still some iron kettles around.

In the first world – use stainless steel pots. Or porcellain. Or whatever. Not unprotected iron. Common sense, really, in all honesty.


All things summed up

OK. I just took five pages to prove that reboiling water is ok.

I’m a hero, really.

Well. What don’t you do for a good and unsolicited rant…