Q. On Shabbos, may one open his window when it is raining even though there are plants on or near the window sill, and he knows for certain that the rainwater will go on the plants if the window is opened?
Does it matter if he wants the plants to be watered, or if he is opening the window because it’s hot, or both reasons?

A. Horav Shlomo Miller’s Shlit’a opinion is that one is not allowed to open a window, if he knows for certain that the rainwater will go on the plants by the window and water them. However, he may open somewhat the window when fresh air is needed, if it is only doubtful that the water may reach the plants and his intention is not to irrigate them but to ventilate the room. He may also cover the plants with a plastic sheet, before opening the window.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit”a