Some people say cold water boils faster than hot water, this is false, [found][1] [here][2] [and here][3].

One reason might be (from the first link):
"Some water heaters may introduce additional sediment into the water, giving you another reason to consider starting with cold—at least, if time is not of the essence."




  [1]: http://itotd.com/articles/521/water-freezing-and-boiling-myths/
  [2]: http://www.scientificamerican.com/article.cfm?id=is-it-true-that-hot-water
  [3]: http://askville.amazon.com/cold-water-boil-faster-hot/AnswerViewer.do?requestId=2758038