One may not intentionally water his lawn on Shabbat (See here.)

A shul congregant told me that he has a sprinkler that waters his lawn based on the weather forecast. It is not set on any type of clock so he is not intentionally setting the system to turn on Shabbat. He says that the system measures the water table in the lawn and combines this with a weather "feed" that it gets from a website. If the lawn is "dry", it will turn on the sprinkler that day. However, if the weather report predicts rain, it will not turn on, as the rain will do its job.

Can someone having this type of system have his lawn watered on Shabbat, or has he violated any melacha?

See this article for an example of this type of system and a brief explanation of how it works.

Please ignore concerns of mar'it ayin for purposes of answering this question.

  • The SA seems to be talking about a person who directly waters the lawn (e.g. by pouring water on it). I don't think it's directly relevant to this question.
    – Daniel
    Sep 7, 2016 at 20:50
  • 2
    Why is it different than the sensors in an air conditioner or heat system? Why shouldn't maaris ayin be a major part of answering this question?
    – user6591
    Sep 7, 2016 at 20:59
  • what can be the prohibition? If you have a pet who eats alone the lawn on Shabbat are you chayav because of kotser?
    – kouty
    Mar 7, 2017 at 21:35
  • I apologize for going off topic, but I'm really curious as to what the product is. Do you know the name or brand of the sprinkler? Jul 6, 2017 at 18:20
  • @Bachrach44 I'll see if I can ask the person in shul who told me about this. I've edited a link, in my question, to one brand.
    – DanF
    Jul 6, 2017 at 18:29

1 Answer 1


Even assuming marith ayin were not a problem (e.g. if it was obvious to everyone that the system is automated), there might still be a problem of conspicuous automated work being done on Shabbath (see hashmaath kol or "avsha miltha"; see e.g. here, see also here)

An additional issue in your scenario beyond those of timers is the reliance on the weather feed which is unlikely to be entirely automated. If Jews are involved, it should be prohibited. Even if only non-Jews are involved, there is a prohibition on a Jew of having a non-Jew perform work on his behalf (see e.g. here). In this case, though, there may be room for leniency based on the principle of ner l'echad ner l'meah (lit: "a lamp [lit] for one is a lamp for a hundred (see here), i.e. if the majority of those benefiting from the non-Jews work are also non-Jews, benefit of Jews is considered incidental, and the work isn't considered as performed on their behalf.

  • If possible please link a source to the "ner l'echad ner l'meah " rule. I don't think hashma'at kol is a concern regarding an outdoor sprinkler, esp. in a primarily Gentile neighborhood. Also, the company providing the service is a non-Jewish company, and the weather feed, from my understanding comes from Accuweather. The only Jew I know there is Ari Salsalari, but he's assigned to the severe storm reporting area.
    – DanF
    Sep 8, 2016 at 15:02
  • @DanF Even if there's not other Jews in the country, it doesn't make hashmo'as kol or Maris ayin any less of a halachik issue. That said, I remember learning that something like a ticking clock or air-conditioner, which is always set before hand, doesn't have the issue of hashmo'as kol. I'll try to verify it. If so, if sprinklers are generally speaking set beforehand (like on a timer), then it's alright
    – user613
    Oct 10, 2016 at 12:13
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    @user613 Re the clock: hebrewbooks.org/pdfpager.aspx?req=16043&st=&pgnum=322.
    – user9643
    Apr 24, 2017 at 6:17
  • Your second source (zomet) doesn't address hashmaat kol at all - did you get the wrong link? More importantly though, you seem to take an approach to hashmaat kol not supported by the sources. The Broyde article you linked to talks about noise. How much noise does a sprinkler make? The article also points out that there is a machloket about whether or not noise is even an issue on shabbat, and the poskim are divided. You present it as an isur without qualification. Jul 6, 2017 at 17:31

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