Study Eruvin folio 89A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
לא שנו אלא שלא עירבו, אבל עירבו — מותרין.
They taught this halakha only with regard to a case where the residents of the two upper stories did not establish an eiruv together, but if they established a joint eiruv, they are all permitted to pour water into the courtyard.
וכי לא עירבו, מאי טעמא לא? אמר רב אשי: גזירה דילמא אתי לאפוקי ממאני דבתים להתם.
The Talmud asks: And where they did not establish an eiruv, what is the reason that the residents who did not dig a pit may not pour water into the courtyard? Rav Ashi said: It is a decree, lest people come to take out vessels filled with water from their houses into the courtyard, to pour into the pit. In the absence of an eiruv, this practice is prohibited.
Text data via Sefaria: William Davidson Edition - English and William Davidson Edition - Vocalized Aramaic, CC-BY-NC; edition provenance: Koren. Display terminology has been modernized for readability.