Tuesday, April 09, 2013

Is water damaged by boiling in a microwave oven?

Last week I received by email a post about the danger of using a microwave oven to boil water. It says that a schoolgirl in England did an experiment comparing water boiled in a microwave oven with water boiled normally.She used microwaved water on one potted plant and normal boiled water on another similar plant. She was shocked that the plant given microwaved water deteriorated daily and died in a few days while the other plant grew bigger and bigger. Photographs of the two plants were provided to show how the plants fared day by day.

I decided to test this story by germinating bean sprouts. I bought a packet of seeds and placed seeds on tissue paper in ventilated transparent plastic boxes.Then I boiled one cup of water in a microwave oven and another in an electric kettle. After the water had cooled, I wetted one box with microwaved water and the other with kettle-boiled water. The seeds began to swell within an hour. Over the next four days the plants grew equally well in both boxes. Here are the pictures taken on the 4th day of my experiment.

The box on the right, with the letter M written on the lid is the one treated with microwaved water. There is no difference between the two sets of plants. In front of each box are two plants removed from each box to show the tallest and shortest plants in each box.  Yes, there was variation within each box.

The second picture shows the bag of seeds from which the experimental seeds were taken,  to show that the seeds all come from the same source.  

The third picture shows all the seedlings taken out from each box and arranged by height. The label M indicates that the bottom row is the one treated with microwaved water. The range of variation is the same for both treatments.
The fourth picture shows the seedlings grouped into small, medium and large size classes. The number of seedlings in each size class is indicated in the labels. I had 77 seeds in the box treated with microwaved water and 71 seeds in the other box. 

Anyone should be able to do this experiment, which illustrates a couple of important principles in scientific experimentation. 

In an experiment comparing two treatments, all other factors except the experimental treatments must be the same. The boxes, the tissue paper, the room and table top, the source of seeds, even the observer, must all be the same. Only the water is allowed to be different. The experiment was carried out in a room that nobody else could enter and disturb.

The experimental materials i.e. the seeds and seedlings in this case, are naturally variable. There would be slow-growers, fast-growers and in-between growers. If we use a small number of seeds we may accidentally have a concentration of small growers in one box and fast growers in the other box and the experiment would fail to demonstrate the effect of the water.The number of seeds (we call it the sample size) must be large enough to override the natural variation. If we do not know what natural variation to expect, we should start with a big sample. In our case, 70 to 80 seeds turned out to be big enough. If we had started out with too small a sample we could not have obtained a clear-cut result. 

Most experiments cannot be run so easily. The materials may be expensive and bulky e.g. coconuts instead of mung beans;subject to stringent ethical and moral controls e.g. humans and animals; require months or years to develop under unpredictable climatic and field conditions e.g. most field crops; impossible to obtains in large numbers from a uniform source. There are ways to deal with all these problems but the basic principles of experiment are the same.

Was the experiment by the English schoolgirl a deliberate fabricatiuon or a poorly planned experiment? I think it was a deliberate fabrication.. 


Tiago said...

Today I am living in a rental furnished apartments buenos aires. I did the same experiment with your same results.

Anonymous said...

Hello Dr.Ng
I've been reading your blog.I'm interested in biochar/horticarbon.Do you know where I can get it besides 1u?Thanks!

deming said...

wonderful experiments

Real Life in Malaysia said...

Hello Dr Ng,

I was led here by "avocado planting in Malaysia" ... that was a very useful entry you had a few years back ... and curious i checked your 2013 only entry and found this ... i am most happy to say that it was a surprise to me that you would make an effort to check the girl's story with your own experiment ... i would like to share both your avocado and taugeh stories with my lovely online young mothers ... thank you ...:)

Real Life in Malaysia said...

... lovely online friends who are also young mothers ...:)

Ammy said...

I think the email you received was completely fabricated in the first place. It's probably yet another urban legend. This is why I hardly read anything forwarded to me by email. We have no idea about the source of such content.

That having been said, I'm glad you did an experiment to debunk what was alleged in that email forward you received. Thanks for sharing.

P.S. I got here while doing a search for your book "Tropical Gardening & Horticulture" - how can I purchase it? I'm reading a borrowed book from the local library right now. I live in Singapore. Fantastic book by the way - I finally know the names of many plants I grow or have come across!

Anonymous said...

Did you used filtered or unfiltered water? In case of unfiltered water from SYABAS, it contain much solid residues. Could microwave alter the solid particles to something harmful to the plants? Also the other variation could be the time the water was boiled/microwaved? The longer it was boiled/microwaved, the more harmful it is? Well this could envisage a PhD project, in more controlled environments and factors using various plants. The results could be suprising.

Anonymous said...

It could be the chlorine in the water. Tap water is chlorinated. When the water is Microwaved, chlorine could be converted to free radicals.
One can use household bleach for chlorine, use just a tiny amount. The roots of seedling should be immersed in water, just like in a hydroponic system. This will allow the free radical to "attack" one seedling rather than many seedlings.
Happy Experimenting.

Unknown said...

Nice Experiment..."Is water damaged by boiling in a microwave oven"

The LawMan said...

Can buy via MPH Online. Paperback. RM89.90. MPH has branches in Singapore so it should be possible to arrange something.

Anonymous said...

Thanks for this experience. Everything should be tested.

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