Is microwaved hot water different somehow?

I just fixed a cup of Theraflu, and noticed the directions state- “dissolve contents into 8 oz hot water. If using a microwave, add contents to 8 oz of cool water, stir briskly before and after heating.”

Why does the Theraflu care how the water gets hot?

If you dump powder into microwaved hot water it can blow up. Really. Or so I’ve read.

I had to go google to find this:

It can superheat in the microwave, and if you add a powder to superheated water, it can boil over violently and KILL YOU TO DEATH.

Microwaved hot water may not boil. Then you put in the powder, and it will boil all at once, seemingly exploding, and then scald you.

Yes, I’ve had this happen to me once when I microwaved some water and then added some salt - POOF!

Fortunately, I wasn’t standing too close…

Superheating water with the microwave.


So this is only a problem if you microwave distilled water, right?

Well, it depends. Some tap water is more pure than others. And people who have filtration systems and whatnot in their houses may have water that is pure enough to superheat.

It’s also a function of how smooth/clean your vessel is. Water needs tiny imperfections to act as nucleation sites to avoid superheating.

the time it happened to me, I was using ordinary tap water.

Great question.

I remember hearing a report that said mircrowaved water is different. Once micorwaved and cooled if it’s used to water plants the plants die. The report also said that observed under a microscope, the crystals of, previously boiled via microwave, water malform instead of coming together the way they ought to.

I can’t remember where I saw or heard this report so I’ll be very interested to hear the answers to this question.

(I already knew about the superheated + powder = deathly explosive potential!)

as mentioned the boiling readily starts at nucleation sites (small irregular points). in a metal pan on the stove top there are usually many scratches that are nucleation sites. in a glass (more likely) or ceramic container used in the microwave there are chances there aren’t many scratches or imperfections in the surface.

you can make a nucleation point to safely prevent super heating by placing a glass stirring rod (like a cocktail stirrer) into the vessel before you heat in the microwave.

as a last resort, you can also before touching the container or adding anything to it and after the microwave has stopped and you have opened it, put a long handled something into the liquid while wearing an oven mitt. do this only at arms reach. if you touch the container with your hand to take it out the boiling could occur and spill onto your hand. if you are close it could splash onto your face.

best to heat only for a time and power that you know will not make the water boil unless you take other precautions.

Wha? This sounds completely bogus to me – water is water, and there are no crystals in water, even if you look really close. If you see crystals, that’s ice, or something else in suspension like sand.

I think you need to come up with a cite for that claim.

Ooops, sorry lazybratsche, my bad.

That should have said "The report also said that observed under a microscope, the crystals of freezing, previously boiled via microwave, water malform instead of coming together the way they ought to.

I was skeptical when I heard it too, so I’m anxious to know whether they were correct or not!

water is only crystalline if frozen. if it wasn’t frozen they weren’t looking at water crystals. if it froze then it came together like it is supposed to.

what kind of microscope? a light microscope can not see molecules.

chlorinated tap water can kill plants if the chlorine isn’t removed, without knowing what they did to the water they may have not removed it.

you would need to cite this. it would feel safe in saying i think this is self published by nonscientists and is bogus.

I keep typing snide comments and deleting them, then typing more and deleting them again.

I’m only a HS science teacher, not a real scientist, but I just can’t imagine what would be the end use difference in water because it had been shaken back and forth by a certain frequency of light/radio. Water is energized all the time by other methods and no one claims this kind of thing for that. Are we then saying that water molecules that have encountered certain amounts of certain kinds of light are essentially NOT water as we commonly know it? They don’t have ten electrons? The electrons are in different orbitals and can’t fall back to ground state? The light has invented a new particle in between the water molecules that inhibits normal crystallization?

I would need a very, very good citation for this.

Microwaving water does nothing to change the very simple chemical composition of H2O.

It doesn’t ionize it or magnetize it. Though it does wiggle the electrons around during the process. The same thing happens when water is boiled on a stove, thought the process is a little reversed. On a stove, the heat excites the electrons. In a microwave, the excited electrons cause heat.

Otherwise the H2O remains H2O and all properties are the same.

As previously mentioned repeatedly, heating pure water in a smooth container without opportunity for nucleation will result in superheated water that will “explode” as soon as given a opening for nucleation such as introducing a spoon or a powder. (the same concept is at work in the diet coke/mentos explosion, but diet coke is not at 212+ degrees farenheit (100+ celcius))

For what it matters you can superheat water on a stove too, its just that very few of us use glassware on a stovetop and metal is never as smooth as glass.

I superheated a mug of black coffee once without realising it.

I grabbed it straight from the microwave and took a glug.


I spat the coffee out immediately, and then the entire first layer of the roof of my mouth sloughed off in a single sheet. Couldn’t taste anything for a week.