Siman 376
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א בּוֹר שֶׁבֵּין חֲצֵרוֹת וְאֵין בֵּינֵיהֶם פֶּתַח אוֹ חַלּוֹן שֶׁיּוּכְלוּ לְעָרֵב, אוֹ שֶׁיֵּשׁ בֵּינֵיהֶם וְלֹא עֵרְבוּ, אֵין מְמַלְּאִים מִמֶּנּוּ בְּשַׁבָּת אֶלָּא אִם כֵּן עָשׂוּ מְחִצָּה עֲשָׂרָה לְמַעְלָה מִן הַמַּיִם. וְצָרִיךְ שֶׁיִּהְיֶה טֶפַח מִן הַמְּחִצָּה יוֹרֵד בְּתוֹךְ הַמַּיִם, וְאִם הָיְתָה הַמְּחִצָּה כֻּלָּהּ בְּתוֹךְ הַמַּיִם, צָרִיךְ שֶׁיִּהְיֶה טֶפַח יוֹצֵא מִמֶּנָּה לְמַעְלָה מִן הַמַּיִם כְּדֵי שֶׁתִּהְיֶה נִכֶּרֶת רְשׁוּת זֶה מֵרְשׁוּת זֶה. וְכֵן אִם עָשׂוּ עַל פִּי הַבּוֹר קוֹרָה רְחָבָה ד"ט, זֶה מְמַלֵּא מִצַּד הַקּוֹרָה וְזֶה מְמַלֵּא מִצַּד הָאַחֵר. הַגָּה: וְדַוְקָא אִם בָּא לְמַלְּאוֹת בְּכֵלִים שֶׁל בַּיִת, אֲבָל בְּכֵלִים שֶׁל חָצֵר לֹא בָּעֵינָן שׁוּם תִּקּוּן דְּהָא חֲצֵרוֹת רְשׁוּת אַחַת הֵן כְּדִלְעֵיל סי' שע"ב (הג"מ פט"ו).
1 Laws of a pit and well between two courtyards. Containing 4 paragraphs A pit between two courtyards where there is no opening or window through which they could make a joint eruv — or where there is one but they did not make an eruv — one may not draw water from it on Shabbat unless a partition ten hand breadths high was constructed above the waterline. A hand breadth of the partition must descend into the water. If the entire partition is within the water, a hand breadth must protrude above the waterline so that one domain is visibly distinct from the other. Similarly, if a beam four hand breadths wide was placed across the mouth of the pit, one resident draws water from one side of the beam and the other from the opposite side. Rema: This applies specifically when one comes to draw with vessels from the house. But with courtyard vessels, no such arrangement is needed, since courtyards are considered a single domain, as stated above in Siman 372.
ב בְּאֵר שֶׁבְּאֶמְצַע הַשְּׁבִיל בֵּין שְׁנֵי כָּתְלֵי חֲצֵרוֹת, אַף עַל פִּי שֶׁהִיא מֻפְלֶגֶת מִכֹּתֶל זֶה ד' טְפָחִים וּמִכֹּתֶל זֶה ד' טְפָחִים, שְׁנֵיהֶם מְמַלְּאִים מִמֶּנָּה וְאֵינָם צְרִיכִים זִיזִים עַל גַּבָּן, שֶׁאֵין אָדָם אוֹסֵר עַל חֲבֵרוֹ דֶּרֶךְ אֲוִיר. הַגָּה: וְדַוְקָא כְּשֶׁאֵין הַחֲצֵרוֹת פְּתוּחוֹת לַשְּׁבִיל רַק בַּחַלּוֹנוֹת (טוּר וְהַמַּגִּיד פ"ג מה' עֵירוּבִין). וְיֵשׁ אוֹמְרִים דְּאִם אֵינָן מֻפְלָגִים אַרְבָּעָה, אוֹסְרִים אֲפִלּוּ בִּכְהַאי גַּוְנָא (בֵּית יוֹסֵף בְּשֵׁם רַשִׁ"י).
2 A well situated in the middle of a pathway between two courtyard walls — even if it is four handbreadths distant from each wall — both residents may draw from it and need no projections above it, since no person restricts his neighbor through airspace. Rema: This applies specifically when the courtyards do not open into the pathway but only through windows. Some say that if the well is not four handbreadths from each wall, they do restrict one another even in this case.
ג שְׁתֵּי חֲצֵרוֹת וּבֵינֵיהֶם ג' חֻרְבּוֹת, כָּל אֶחָד מֻתָּר בְּאוֹתָהּ שֶׁאֶצְלוֹ לְהִשְׁתַּמֵּשׁ בָּהּ דֶּרֶךְ חַלּוֹנוֹת עַל יְדֵי זְרִיקָה, וְהָאֶמְצָעִית מֻתֶּרֶת לִשְׁנֵיהֶם. וְאִם הָיוּ שְׁלָשִׁתָּן סְמוּכוֹת לַבָּתִּים, שֶׁהָיְתָה הָאֶמְצָעִית כְּנֶגֶד הַשְּׁתַּיִם כִּשְׁלֹשָׁה רָאשֵׁי קַנְקַן, כָּל אֶחָד מֻתָּר בַּחֻרְבָּה שֶׁאֶצְלוֹ וְהַשְּׁלִישִׁית הַקְּרוֹבָה לִשְׁתֵּי הַחֲצֵרוֹת אֲסוּרָה לִשְׁתֵּיהֶן.
3 Two courtyards with three ruins between them: each resident may use the ruin adjacent to his courtyard — through windows, by throwing — and the middle ruin may be used by both. If all three ruins were adjacent to houses such that the middle ruin faced the other two in the arrangement of three points of a tripod, each resident may use the ruin on his own side, but the third ruin — which is close to both courtyards — is forbidden to both.
ד בֵּית הַכִּסֵא שֶׁבֵּין שְׁנֵי הַבָּתִּים וְלֹא עֵרְבוּ יַחַד, רְשׁוּת שְׁנֵיהֶם שׁוֹלֶטֶת בּוֹ וַאֲסוּרִים. וְעַיֵּן לְעֵיל סי' שנ"ה.
4 An outhouse situated between two houses that did not make a joint eruv: both parties have jurisdiction over it and it is therefore forbidden to both. (See also above, Siman 355.)