Future action in main clause

Question

Your explanation below is quite clear. However, the answer is the imperfect, not the imperfect subjunctive. Is this an error, or what am I missing?If the main clause uses a tense or a mood that implies a future action, for example El Imperativo  or El Futuro Simple, then the por si/por si acaso clause uses El Presente (probable) or El Pretérito Imperfecto Subjuntivo (less probable)

Answer

Hola Peter
It needs the imperfect subjunctive. This is the example that the lesson shows in that bit:

Poneos las botas de agua por si lloviera.
Put the wellies on in case it rains.

"Lloviera" is the imperfect subjunctive, not the imperfect indicative.Saludos