I took about 100 ml of distilled water, put a small, clean rock in it (to prevent "bumping" or explosion) and heated it repeatedly in a microwave oven on high for 45 seconds. After each heating I checked the temperature of the water with a digital temperature probe. I did this 7 or 8 times. I saw bubbles coming off of the rock and the sides of the glass. The highest reading I ever got was 93.5 degrees C. I gave up when the quantity of water become noticeably reduced (50%). So, I thought, the thermometer must be off. So I boiled tap water in a large pot to roiling and checked the temperature with the probe. 99.5 degrees C was the highest value I could read. That's about right for my altitude. My question is why was the boiling point in the microwave lower? Shouldn't it have actually been higher due to superheating? Does this have anything to do with hydrogen bonding (or the breaking of hydrogen bonds)?