Talk:Decomposition temperature

When boiling cold tap water for a fresh cup of tea or coffee - I use a whistling glass kettle(freshly cleaned with hydrochloric acid to remove any sediments or deposits, and I find that if I leave it boiling away for too long or simmering away for too long, then the water appears to break up or curdle, with lots of transparent white stuff dispersed throughout it. Naturally at this point, I thhrow it out and start again, remembering to pour my cup of tea, immediately as the water comes to a boil. Could this be some kind of decomposition due to the hardness of the water or any impurities contained therein? Has anyone else noticed this? Is there an explanation and can this be avoided? - Not to be confused with the break down of water into hydrogen and oxygen when heated to 2000'C