721. Pouring into a Gutter or Drain

Shabbos 15:18

Let’s say that there’s a drain into which water is poured and through which it flows underground into a public domain, or a gutter where water is poured and it flows down a wall into a public domain. Even if the wall or the distance underground through which the water passes is 100 cubits long (about 150’), it is prohibited to pour into the mouth of this drain or gutter because one causes the water to flow into the public domain. Rather, one should pour water outside the drain, letting it flow into the drain on its own.

Shabbos 15:19

The above halacha applies in the summer; in the winter, one may pour water as discussed in 15:17. One may even do so repeatedly, without hesitation. In the winter, the gutters are already flowing with water that one desires to be absorbed in its place. One is permitted to pour water into a drain that flows into a carmelis, even in the summer. No restriction was enacted against pouring into a carmelis. This is why one may pour water down the side of a ship and into the sea.