Commentaire sur Erouvin 8:9

אין שופכין לתוכה מים בשבת – that in the four cubits, the water that a person is used to using on each day is absorbed there in their place, and doesn’t go out into the public thoroughfare, but less than four cubits, the waters are not absorbed in their place and go out to the public thoroughfare.

Introduction Whereas the previous mishnayot dealt with drawing water from cisterns or streams, today’s mishnah deals with pouring out water inside a courtyard. The problem is that this may be considered taking something from the private domain and moving it to the public domain. Our mishnah deals with when this is considered a problem and when it is not.

עוקה – hole.

A courtyard which is less than four cubits: they may not pour out water in it on Shabbat unless they made a trough holding two se’ah from its drainage point downwards, regardless of whether [the trough] was outside or inside, except that if it was outside it is necessary to cover it and if it inside it is not necessary to cover it. In a courtyard which is larger than four square cubits, the sages allowed one to pour out water because they assumed that the water would be absorbed in the ground and would not make it out to the public domain. Even if the water should escape to the public domain, since the person didn’t intend to pour water from a private to a public domain, he has not transgressed any commandments. However, the sages prohibited pouring water out onto the ground in a courtyard smaller than four square cubits lest the water goes from the public to the private domain. He is allowed to pour water out onto the ground in a small courtyard if he makes a drainage trough to catch the water before it goes out to the public domain. The trough must be able to hold at least two se’ah of liquid (about 24 liters), which the sages estimated to be the average amount of water that a person would use in day. The drainage point was at the top of the trough, to allow overflowing liquid a way out. The mishnah teaches that the trough can either be in or outside the courtyard’s walls. Even though if it is outside the courtyard, it is in the public domain, it is still not considered part of the public domain. However, if he makes it outside, he must cover lest he make the trough four by four handbreadths wide and three handbreadths deep in which case it is a karmelit. It would be prohibited to pour water from a private domain (inside the courtyard) to a karmelit. If he covers it, it is no longer considered a karmelit. If he makes the trough inside the courtyard, like the courtyard, the trough is also a private domain and there is therefore no need to cover it.

מחזקת סאתים – because a person usually consumes two Seah of water a day (from the supply in the cistern – see Talmud Eruvin 88a).

מן הנקב ולמטה – so that the hollow of the hole supports two Seah prior to the water reaching the perforation that is on its rim that causes an uninterrupted flow into the public thoroughfare.

בין מבפנים בין מבחוץ – whether he made the hole in the courtyard or whether it was made in the public thoroughfare.

צריך לקמור – to make upon it a kind of arch covering from above in order that it is separated from the public thoroughfare.