Why is it important to know how to boil water? Won't any hot water do for cooking? Can't I just use hot water from the tap?
No.
Recipes call for things to be hot, to be simmering, to be boiling or to be brought to "a rolling boil." Failure to follow these specific instructions can make things taste awful! Foods like rice or pasta will not cook correctly!
The tea will not steep!
Black teas and herbal tea will not steep right unless the water is at the right temperature. It will taste like blah hot water with some sort of flavoring in it (I realize there are specific temperatures for specific teas, and I won't go into that in this post). The hot water coming out of the regular kitchen tap is nowhere near boiling temperature. What that hot tap water is good for, is filling into the teapot to warm it up while you are waiting for the water in the tea kettle to boil. Once the tea kettle water is boiling, you can dump out the tap water from the teapot and then make the tea with boiling water, without the fear of your teapot cracking.
Why is it important to go on and on about this? As someone who likes milk in my tea, which cools it down, I like to start with a really hot cup of tea. Otherwise when I pour the milk in, I get a lukewarm serving. The way I see it is, if you can place your hand on the teapot and hold it there for even a second, it isn't hot enough.
So on to how to boil water!
First, use cold tap water. Cold. Not lukewarm, not warmish and NOT hot!
Run the water for a while before filling your kettle-- it will also get the "sitting in the pipe" flavor out of the water-- and will be nice and cold.
Now, set the pot or kettle of cold water on the stove and turn the burner on to "high." A lid on the pot will help it to heat up faster.
See the steam coming up from the water? It isn't boiling. It's hot but it isn't boiling, so do not pour this into the teapot yet! Or put in the pasta yet!
Aha-- see the bubble in the middle of all that steam? It isn't boiling. Don't use it yet.
Now there are lots of little bubbles-- and it even sounds noisy. Don't turn off the burner! It isn't boiling yet! You can tell the water is boiling when it quits making noise and starts to be quiet. If you do not have a tea kettle with a whistle, please resist the urge to turn off the burner because there is noise in the kettle. It isn't ready yet!
Rapid little bubbles means it is simmering.
Now you can see that the water is boiling. That is, large bubbles racing up to the top of the water.
And here we are getting to the rolling boil. A rolling boil may be called for in some recipes. If you start out with a good rolling boil for some cooking, the water will return to a boil very quickly after you put the food in (Sometimes recipes say to bring water TO a boil. In that case you don't want the water to go on and on and on before using it).
Boiling water is turbulent--
like a stormy sea--
When you lift up the kettle to pour it into the teapot, and you can feel that the water is still moving inside, then that is a good strong boil. And now you are allowed to use it to make that lovely, hot pot of tea!