I purchased this book "The way of tea" while I was in Hong Kong last year. Written by Lam Kam Cheun, this book is a general book on chinese tea. The book mainly deals with tea history, types of tea and tea making with a chapter on healing teas. The book has beautiful illustrations and pictures and makes worthwhile reading for the avid tea drinker.
One of the articles in the book deals with the optimal temperature of water to make tea. The author describes the 3 ways of distinguishing the water temperature; namely Shieng Pien (by sound), Chi Pien (by watching the steam) and Hsing Pien (looking at the bubbles).
Click on the 2nd pix to have a enlarged view of the different bubbles of boiling water. In the 1st level of boiling water, the bubbles are called crab eye bubbles, 2nd level - fish eye bubbles, and the 3rd level - old man bubble. Fish eye bubbles is the right temperature for most teas (pu erh, oolong, tky, red tea). Other teas like green and floral teas require slightly cooler water leave fish eye water to cool for 1-2 min). The writer explained that the 1st level (crab eye) is called yin yang water and "is never used for anything in cooking as yin yang water is said to be unhealthy." The writer also commented that "at the third level, the water bubbles like mad. This is called old man water or white hair water and is not used for making tea."
Well next time when you boil water, look at the water bubbles closely....not too close or else...steamed eye.