Commentary for Bava Metzia 153:18

Before in the case of the river overflowing, he didn’t differentiate between if it was likely to overflow or it was not likely to overflow, because, you would think that he would only have agricultural ditches if it was needed regularly, so it must be that the river overflowed regularly (Why can’t we just say that the ditch is just to make it easier for the workers, that they can just put the water from the river right into the ditch? We have to answer that ditches are only made for when the river overflows, and not just for workers). And he doesn’t differentiate between if they are from the city or not, because even if they are from that city, it would still be the Ba’al Habayis’es loss. Because, it is not their problem to know how his field works, if it has ditches or whatever. So, if the river overflows, only the ball habayis would that HIS field was watered. But if the river stops, the whole city would know.