Question: When using an electric water cooker/boiler, how to translate the following:

> 
> The water is boiling.
> 
> 
> 

What would be arguably the most common way in Mandarin to say this in Taiwan?

Answer: 
> 
> "The water is boiling."
> 
> 
> 

We say 水開了 in Taiwan. Nothing else.

我們都說「水開了」，好像沒有人用其他講法。
“水開了/沸了/滾了” are all used in oral. Even “水好了” goes well (好了=燒好了, and you can use it in preparing for bath, either).