Structure of zero conditional

Structure of zero conditional
positive negative question
If/when you heat water to 100 degrees, it boils. If/when you don't heat water to 100 degrees, it doesn't boil. What happens if/when you heat water to 100 degrees?


The zero conditional – common mistakes
Common mistakes Correct version Why?
If people eat too much, they will get fat.
Water boils when it will reach 100°C.
If people eat too much, they get fat.
Water boils when it reaches 100°C.
We use the present simple in both clauses of a zero conditional. We are saying that the condition is always true.
If/when you don’t exercise, you get fat. If and when have the same meaning here. We can also use whenever.