Then you've misunderstood mine, unless you're basing this on David's.
"As you boil water, the water turns into vapour in the air."
(Pardon me for adding a few necessary words).
Yes, this is the meaning of "As" that David was asserting. Apparently he regards it as the only way to use "As".
"When" means a similar thing here", though it doesn't emphasise the simultaneity of the boiling and the vapourising.
"If" doesn't enter into it. (The water could be evaporating).
How do you feel about "As the water was boiling, I added some salt".
Student or Learner