Related for Berakhot 7:5
שְׁתֵּי חֲבוּרוֹת שֶׁהָיוּ אוֹכְלוֹת בְּבַיִת אֶחָד, בִּזְמַן שֶׁמִּקְצָתָן רוֹאִין אֵלּוּ אֶת אֵלּוּ, הֲרֵי אֵלּוּ מִצְטָרְפִים לְזִמּוּן. וְאִם לָאו, אֵלּוּ מְזַמְּנִין לְעַצְמָן, וְאֵלּוּ מְזַמְּנִין לְעַצְמָן. אֵין מְבָרְכִין עַל הַיַּיִן עַד שֶׁיִּתֵּן לְתוֹכוֹ מַיִם, דִּבְרֵי רַבִּי אֱלִיעֶזֶר. וַחֲכָמִים אוֹמְרִים, מְבָרְכִין:
Two groups who ate in one house — if some of them see each other, they join for zimun; and if not, each group makes a zimun itself. [And if one waiter serves both groups, though they do not see each other, the waiter joins them.] One may not make the blessing over wine [borei p'ri hagafen] until he dilutes it with water. These are the words of R. Eliezer. [For their wine was very strong and was not fit for drinking until it was diluted. Therefore, (before being diluted) it was not "changed for the better" and did not depart from its original blessing, "borei p'ri ha'etz," for grapes. But the halachah is not in accordance with R. Eliezer.] And the sages say: One does make the blessing.