Yes, you NEED to know this. Why? Because not knowing a rolling boil from a shimmer or a simmer can make or break your dinner. Always start with cold water. You may think using hot water will make things faster, and it will, but you'll be ingesting all kinds of sediment that has been lying around it the hot water tanks. Think about it people, most of you live in NYC and trust me, you have enough toxins to wade through during the day without eating "mystery minerals."