Reheat Water - your opinion!

Nope, I don’t think so. Once you bring water close to a boil the dissolved oxygen is practically zero. Further boiling does not reduce it further. There may be other reasons not to reboil water but DO is not one of them. Feel free to refute the below but if so you’re going to have to provide better sources than “a chemist”:

“The dissolved oxygen hypothesis rests on two premises: (1) that once-boiled water contains more dissolved oxygen than twice-boiled water; (2) that dissolved oxygen improves the flavor of tea. Both premises are demonstrably false.

Boiling itself does not remove dissolved gases. It is the change in temperature or pressure that affects the amount of gas that a liquid can hold (i.e., the solubility of a gas in a liquid). Solubility decreases as temperature increases. Assuming normal atmospheric pressure and composition, water at 0˚C can hold a maximum of ~15ppm DO, while water at 50˚C can only hold ~5ppm. Once the water reaches 100˚C, solubility is zero. Therefore, if you’ve brought water even close to a boil, you’ve removed virtually all the DO. What this means is that neither once-boiled nor twice-boiled water contain significant levels of DO, refuting premise (1)."

Source: http://hotwatermagic.blogspot.se/2013/04/destructive-myths-dissolved-oxygen.html

And here is Stanford Magazine (they do not mention DO, but that’s the point, they do not mention DO):
“The warning against reboiling water probably goes back to days when water sources were more suspect. Boiling water kills potentially dangerous microbes and parasites, but it can also concentrate inorganic poisons. If you’re using clean water, you can reboil it as many times as you want—it won’t affect the taste or your health. However, if your water comes from a well, all bets are off. Some ground water contains nitrates, found in fertilizer, and arsenic, which may occur naturally or as runoff from farms and industry. Boiling water increases the concentration of those contaminants. The more times you reboil the water, the higher the concentration and the higher the risk.”

Source: https://alumni.stanford.edu/get/page/magazine/article/?article_id=29243

I mentioned this below but the chemists of /r/chemistry disagrees with your chemist: https://www.reddit.com/r/chemistry/comments/7c3tbm/reboiling_of_water_effects_and_dissolved_oxygen/

I’ve heard the same, problem is that I have also heard that the dissolved oxygen reaches almost zero pretty much instantly at a boil. In which case this hypothesis is incorrect. I’m trying to look into this but I am skeptical to the dissolved oxygen hypothesis. I also have never seen anyone posting any evidence whatsoever that dissolved oxygen levels would actually affect taste, so this is all anecdotal.

That said there might be other things that happens with a reboil, like a concentration of salts and minerals. This would be harder to predict since it would depend on the water source and kettle/boiling method.

If you notice I said it was pretty much a matter of preference.

I did notice, but the question whether the tea will be “flat” or whatever is not really a matter of preference, is it? That’s an empirical claim, if one choose to make it.

I think it may be a matter of just how sensitive your taste buds are. Some people may notice a difference, some may not.

Yes, that is entirely possible.
However, I think it would be interesting to know, as a start, if there is a chemical mechanism in place to facilitate such differences. What I am reacting to is that so many people (I am not pointing a finger at you here) make a lot of assumptions without any evidence. One such assumption is that “low oxygen content makes tea flat”. Okay, maybe so. But how does anyone know that? I would love to see some evidence.

I have been told it is bad to reheat the water by people who know more about tea than me, such as my local tea shop owner.

I mean you shouldn’t use hard water for good tea anyway. But you are right – IF you use hard water then the water itself after boiling it once gets quite foggy and you notice that the structure isn’t clear anymore.

But if you take the best source of water (soft, right ph level, not massive in amount of minerals etc.) then the reheating has no impact I would guess – and like you mentioned correctly if you pour water from a certain height into the pot it already collects oxygen again.

So I am really wondering what exactly might be the reason for this believe that reheated water (even if it is perfect water) is bad for your tea! Because if you read about the reason mentioned in certain tea books they might sound more esoteric than scientific like “The water loses its liveliness!”

And like “Tea for Steve” already mentioned: If it is boiled once where is the liveliness after being boiled? And what would make a difference being boiled twice?

The mystical purity of freshly boiled water?

Oddly my mom feels the same way about water for tea. She’s been a lifelong black tea (hongcha) drinker.

“This study states boiling at regular atmospheric pressure is not effective at removing dissolved oxygen.”

So what? What is the definition of “not effective” and how does it relate to tea? I don’t see that the study you linked say anything about the difference in dissolved oxygen content between boil 1 and boil 2 when reheating. There are so many assumptions being made that I have not seen any evidence for, including the basic assumption that dissolved oxygen levels (if the level really IS different after a re-boil, which I also have seen no evidence of) would actually affect the taste.

https://sciencing.com/remove-chlorine-from-water-4516999.html

Boiling will remove some chlorine, but chloramine is trickier

Thanks for the tip. Turns out my water supply uses chloramine, so my letting it sit isn’t doing any good. :( On the up-side, I can’t tell the difference between my tap water and spring water, though I think I’m going to have to have another round of tests.

I’ve found my tap water in HK to perform better than Volvic. Nobody believes me! Lol. So yes I do believe you may not be able to tell the difference

I recently did a small test and didn’t like the water with high mineral content. It had high sodium though which threw my dancong way off. I will try more too soon.

When I was younger I would always use fresh water every boil. I was very particular about my tea method and could taste a difference even without knowing any science.

I can’t taste a difference now but I’m also drinking varied teas compared to younger me drinking the same brand

I think that’s part of it. I do gong-fu most of the time, and every steep is different.

i have been thinking about it, I used to like my tea very clear and hard, like glass. I didnt like it flat or milky.

The taste improved upon these preferences for harder tea with a fresh boil. 100% sure of that

Lauretana good…but if you wanna go all in and fancy, choose Fiuggi!

But hey… so do you think that our tap water here in Vienna is not acceptable?

Not really! It is good drinking quality but definitely not good for high quality tea. I mean if you’re having a cold and want to drink herbal tea then it is totally fine but not like I said for high quality tea. The problem with our water in Vienna at first is chalk. If you’re using porous clay pots it will totally ruin them after a certain time because a layer of chalk will build up and clog the natural flow. Beside that in many older buildings there is still an amount of lead into the water because of the old pipes. Then our water isn’t soft enough it may also not be hard as hell but far from good. But the best way is to test it yourself: Do a side by side tasting with the same tea, same amount of water and tea ratio and one with Vienna water and the other one with Lauretana. I sure you will be amazed by the outcome. With Lauretana a lot of the subtle notes can develop while they are suppressed by our tab water :)

I had a lot of trouble shaving in Wien…The water was surprisingly hard.