Have a look at this experiment using stove and microwave boiled water. http://www.rense.com/general70/microwaved.htm
That's why mine is so small and enlargement emails don't help. I have to stop drinking microwaved water.
No conclusion about toxicity can be drawn by this experiement. Plants need minerals (e.g. nitrogen, potassium, calcium, magnesium) to grow and it is most likely that these were simply present in less quantity in the microwaved water. "Purified" water (was this just filtered or distilled?) is a bad choice for watering plants for this very reason.