Grammar 1.1

Grammar 1.1
Conditional type 0

IF CLAUSE                                             MAIN CLAUSE
If/When + Simple present                     Simple present
 If when you heat water, it boils.

Use: to express a general truth or a scientific fact. In this type of conditional, we can use when instead of if.
When the if-clause preceds the main clause, we use a comma to separate the two clauses. Compare:

If you heat water, it boils.            Water boils if you heat it.