I have seen this story a couple of times in my facebook newsfeed and it strikes me as highly unlikely. The story goes:

Below is a Science fair project presented by a girl in a secondary school in Sussex. In it she took filtered water and divided it into two parts.

The first part she heated to boiling in a pan on the stove, and the second part she heated to boiling in a microwave.

Then after cooling she used the water to water two identical plants to see if there would be any difference in the growth between the normal boiled water and the water boiled in a microwave.

She was thinking that the structure or energy of the water may be compromised by microwave.

As it turned out, even she was amazed at the difference, after the experiment which was repeated by her class mates a number of times and had the same result.

enter image description here

So does microwaved water kill plants?

Is there any structural difference between water boiled on a stove top and water boiled in a microwave?

(Bonus points for confirming/debunking any other statements in the original article. Please cite sources of evidence.)

  • This is a twist on the flawed "Wifi stunts plant growth" experiment. skeptics.stackexchange.com/questions/16479/…
    – nico
    Sep 30 '13 at 7:04
  • 6
    sample size n = 1
    – wim
    Sep 30 '13 at 12:10
  • 1
    Yes! Any boiling water kills plants! Jun 11 '14 at 14:08
  • "Then after cooling " Jun 11 '14 at 22:21
  • My favorite of the students inherit assumptions is that which assumes that water, effectively immutable, is not exposed to all sorts of radiation on a daily basis in nature (including ionizing radiation, of which microwaves are not) Aug 18 '16 at 4:28

Microwave radiation and water

"She was thinking that the structure or energy of the water may be compromised by microwave."

This was debunked by snopes.com.

There is no difference in the water heated by microwaves compared to water heated by another source (like a gas flame, or electric element).

Microwaves are non-ionizing radiation, so do not alter the substance other than exciting it to higher temperatures. (Wikipedia:Non-ionizing radiation)

From cancerresearchuk.org:

Nonionising radiation has enough energy to move things around inside a cell but not enough to change cells chemically. The radiation from a microwave oven is nonionising.

From Australian Radiation Protection and Nuclear Safety Agency:

Nonionising radiation is found at the long wavelength end of the spectrum and may have enough energy to excite molecules and atoms causing then to vibrate faster. This is very obvious in a microwave oven where the radiation causes water molecules to vibrate faster creating heat.

Skeptical analysis of the experiment

This was not a useful experiment. Using a sample size of 1 for each population is akin to the fallacy of using anecdotal evidence. This is just one instance in which one plant died and another lived. The dead plant could have had poor genes, an infestation, poor soil quality, among other things. The container they were using for the microwave water could have been contaminated with something, or used for other purposes in between waterings.

The description of the experimental method, especially the measures they took to avoid causing a difference between the two populations is extremely lacking.

The experiment which was repeated by her classmates a number of times and had the same result.

How many times? Two? Three? 300? Without more detail, this is just hearsay. And again, the story fails to describe the measures taken to prevent other causes of differences between the two populations.

  • 1
    The claim is that this was water. But yes, that is yet another factor that was not well-controlled in this experiment.
    – user5582
    Sep 30 '13 at 6:51
  • 3
    Heating the water in a pan on the stove could add just the trace elements missing in the soil...
    – DJohnM
    Oct 1 '13 at 0:13
  • 2
    @User58220 Yes, that is a possibility. Their contamination controls were not explained.
    – user5582
    Oct 1 '13 at 1:27
  • 2
    The more amazing the result, the less likely the study was blinded. Oct 10 '13 at 17:01
  • 4
    I guess if any public-spirited parent had baby twins they could try this with milk ;)
    – Benjol
    Nov 22 '13 at 9:28

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