Tip: in your current phrasing, your question seems like a rather abstract physics questions. You could get more informative answers if you expanded it to let us know what you are trying to prepare at a certain water temperature. Is it tea perhaps?
But to try to answer the first part of your question as stated: the Rouxbe cooking school has a video lesson demonstrating how you can identify different water temperatures without using a thermometer. For example, for the poaching cooking method (which is done in water at 71 to 85 degrees Celcius) you should look for the first small bubbles at the bottom of the pot and the first signs of steam from the surface. So assuming that the water is at 100 degrees Celsius as soon as you see steam forming is not necessarily correct. For a vigorous boil (100 degrees Celcius, which is the maximum temperature that water can reach at sea level) you have to wait until the water is moving and steaming faster, with big bubbles appearing on the surface.