Here at the office we have a coffee maker used strictly for heating tea water. If I draw water straight from the tap and microwave it to a boil, when the teabag is put in the water, the water accepts the tea bag and placidly makes tea. On the other hand, if I take water from the coffee maker and microwave it to a boil, when the tea bag is put in the water, a violent eruption occurs throwing up to one third of the water out of the cup. ... and asked for guesses as to the cause of this outcome. I received many more responses than expected and so I will try and tie this up with some confirming test results and environment data. Most of the responses I got, (some by e-mail) suggested either super- heated water, or low dissolved gas. I believe both theories work together to provide the results I'm seeing. Using information supplied by people in Netland, ( Thank you all who replied! ), I've made the following environmental obervations: The point which I call boiling is when the surface of the water is releasing large bubbles at a rapid rate. The freshly oxygenated water from the tap will of course come to a boil first and never get a chance to reach the superheated range. The coffeemaker water is kept right on the edge of boiling. If a fresh pot is poured through, the carafe simmers on the warming plate for a while (driving out dissolved gases) and then settles down. If sugar is put into the coffeemaker water before nuking... no reaction results. If the sugar is put in after the nuking... the same reaction is started by the sugar as is started by the teabag (without the sugar). The starting temperature of the cup makes no difference. I tried preheating the cup by nuking the tap water to boiling, letting it sit for a minute, and nuking it again. The structure of the cup is not affecting the outcome (flash heating.) The cup is clear glass and never gets hotter than the liquid. Although I do have pressed wood bowls at home that get twice as hot as the food in them. Water from the coffeemaker makes darker tea faster. Probably less dissolved gas getting in the way. It doesn't matter if you use Lipton or Salada! Again Thank you to all who replied...  - Dan