Microwaved water can kill plant? Meh, just a fiction!

Atistarn Arunaramwong 55010028


           Have you ever heard of an evil machine that can easily pollute your food? Or decrease your lifespan with cancer? That is a rumor of something we called “Microwave oven”.  If you don’t have a clue about this, take a look at these pictures.

Above is a science project, done by a high school student that had been forwarded through email. As you can see, after days of watering plant with microwaved and purified water, the microwaved one died out while the purified one still lived. It claimed that microwaved water can kill plant, according to the pictures. Furthermore, it suggested that eating microwaved food can cause cancer or brain damage. To prove this, we, the student of DSS, conducted the experiment of our own.

The experiment

There are some differences in our experiment. We used rice for the plant and grew them in 3 different pots. Each pot differed with the types of water that resulted in the growth of plant. The first pot was watered with tap water, second with kettle-boiled water and third with microwaved water. All of the water was cooled before used on plant. The growth was measured by the height every week, for 5 weeks. And here is the result.

Time (week)	Average height (cm)
	Tap	Kettle-boiled	Microwaved
0	20.25	20.25	20.25
1	25	23.375	26.75
2	29.75	28.25	34.875
3	31.5	32	39.25
4	32.375	40.75	39.75
5	46.5	47	58.5

Having trouble with numbers? We can make it more understandable with a graph.

And here is a picture to prove it.

As you can see, the third pot is the highest one while first and second are approximately the same. Moreover, rice in the third pot produces grains while others couldn't.

From this experiment, it turns out that microwaved water didn’t kill or damage the plants, but instead increase their growth. What really happen? What kind of property does the microwaved water really has?

            First, we have to know what “microwave” is. Microwave is an electromagnetic wave that has frequency within 0.3 – 300 GHz. It can easily reflect with the metal surface and transmit through non-metal one. But if the substance has water within, microwave will be absorbed. That is how food can heat in the microwave oven.

            So when we boil water with the microwave oven, the oven will radiate microwave with frequency of 2.45 GHz. The wave will go through water molecules that make the water hotter. This method is called a dielectric heating.

           

                 Dielectric heating can only occur with conductive substances. Fortunately, our water is conductive, so we can easily heat up our food. When electromagnetic wave go through water molecule, the particles inside will be vibrated. And the vibrated particles will continuously hit with each other, heating up the water as a result.

                Aside from heating up, microwave didn’t cause any other effects to water.  All the microwave do is spin the molecules around and cause them to bump into each other, but nothing else. So, the microwaved water didn’t kill the plant by all means.

                But don’t trust us so easily like you trust the forward-email. There are also other experiments about microwaved water effect on plant that has reliable results. See https://www.youtube.com/watch?v=x9Us_jMV8hA , an experiment conduct by MythBusters. Or you can try this at home to see it with your own eyes!

References:

1.       Banik, S., S. Bandyyopadhya and S. Ganguly. 2003. Bioeffects of microwave – a briefreview. Bioresource Technology 87 : 155 – 159.

2.       Pozar, David M. (1993). Microwave Engineering Addison-Wesley Publishing Company. ISBN 0-201-50418-9.