Breakdown of Si la lluvia entra por la ventana, la revista puede estropearse.
Questions & Answers about Si la lluvia entra por la ventana, la revista puede estropearse.
Spanish often uses the present tense after si when talking about a real or possible condition in the present or future.
So:
This is a normal, real possibility, not a hypothetical or impossible situation.
English sometimes uses present tense here too: If it rains / If the rain comes in...