When I am brewing tea, I bring the water to a boil before I pour the water over the tea leaves. If the tea were too strong (because, for example, I had let it steep too long), I would probably just say that I needed to "add some water." My audience would understand that the water would be "very hot."
I would really appreciate it if you could give me as many examples of when you use "hot water" and "boiling water" as possible. For my language does not have equivalent words to those two and I cannot distinguish the difference between them.
When water is "boiled," it means that it comes to the boiling point and begins to change from a liquid to vapor (giving off a lot of steam). "Water boils at 100 degrees Celsius." See some pictures of boiling water HERE.
Hot water is water at a lower temperature than boiling water.
If you need more clarification, may I suggest that you google "hot water" and "boiling water." Both phrases are used literally and figuratively in many ways.
If you are making the water hot enough for boiling and are using water in a pan on the stove, make sure that the water boils before you pour it over the tea. To reheat tea that is too strong, you will have to guess whether you need water hot enough to boil or whether water heated will be enough. There is no rule. It is a matter of your taste or feeling about it. Joelline uses boiling water. That is her feeling about it. My wife uses water of any temperature. I use hot water. If serving several people you would be a thoughtful host if you ask, "Is the tea too strong? I can add some water. Do you want it boiled?"