Boiling water multiple times is bad?

Considering that the water you're boiling today has boiled off or otherwise transpired off into the atmosphere and recondensed back to earth probably millions of times by now over the last few billion years, and it's still the same old water, that sounds highly doubtful. Boiling doesn't change its molecular structure. Sounds like something an infomercial would say--was it the Ronco guy that told you that?

Nope, boiling won't change water.

It might affect other chemicals in the water and depending on what you are boiling it in, it might add chemicals. The water will boil long before you release any chemicals from any kitchen pan. Boiling water is a way to purify it and eliminate harmful bacteria.

It is possible that the reference is to the oxygen which is released per boil.
I know posh (sophisticated) tea drinkers insist that the water must be fresh before boiled for tea.

Boiling will result in vaporization of some of the water, driving it off as steam, thus reducing the volume of the original sample, commensurately increasing the ratio of minerals, contaminants and impurities to liquid in the remainder. More or less, what happens is you concentrate the stuff that is disolved in the water; it remains as water evaporates, or steams off.

On the other hand, to purify water, it can be converted to steam, the steam then cooled to condense back into liquid water, and the result - water less insoluable residue, can be collected as purified water, the process is known as distilation, and essentially the same process is employed in the production of alcoholic liquors, the object being to increase the alcohol content, or ratio, of the subject liquid.

I heard the oxygen theory as well - it's better to keep as much O2 in there as you can - dunno why though.

By the time water boils, there's precious little oxygen dissolved in it.

I imagine that's so.

Which was the point, I think, re flavor re food... or something like that.
I too remember something about not boiling water too many times, but not in what context.

I've often heard you should almost boil water for tea and coffee - that you should take it off the heat just the moment before it boils - how would one know?

For everybody: you may want to look for "Dissolved oxygen" on google. Water molecules don't break in H2 and O so they are in the same ratio in the boiled water. It is simpler to understand if you think why you need to add oxygen to the water for the fish in an acquarium.
Regarding making tea, it would be better to do it with freezing water, or, indeed, at least not to boil it. The colder the water, the more dissolved oxygen in it!
Hope this helps

havent heard that but, if you use a metal pot or Al cookware, several boilings can make the Water dissociate more easily and cause some disolving of the metal?
HOLY CHRISE< THIS THREAD IS 10 YEARS OLD!!

Farmerman: I know, I just deleted my brilliant comment. LOL

Heck, I like these old threads that keep popping up (which I seem to have missed the first time around).

I would point out that you breathe with your lungs... so unless the water is going into your lungs, the amount of dissolved oxygen is irrelevant (although apparently it gets some people to overpay for fancy bottled water).

It certainly could be relevant for brewing, though. Oxidation of sugars and amino acids in teas could affect that flavor in a significant way -- perhaps similar to Maillard reactions in cooked foods -- and I'm pretty sure that oxygen is a decent oxidizing agent...

Re-boiling water is like playing Russian Roulette. It's all fun and games until your brains are sliding down the kitchen walls.

I don't play Russian roulette in the kitchen.

Then it's called Hungarian Roulette.

Get your roulettes straight, son.

Wait -- it's Hungarian roulette in the kitchen, or anywhere but the kitchen? Because I'd much rather lose at Hungarian roulette than Albanian craps...