Study Eruvin folio 89A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
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.
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
Mishnah: All the roofs of the city are considered one domain. It is permitted to carry from one roof to another, even if the residents of the houses did not establish an eiruv between them. The rabbis did not prohibit carrying between roofs, as it is rare to transfer an item from one roof to anoth
R' Shimon says: Roofs, courtyards, and enclosures are all one domain with regard to vessels that were inside them when Shabbat began, and one may therefore carry from one of these areas to another. However, they are not one domain with regard to vessels that were inside the house when Shabbat began