Sotah, Chapter 4, Mishnah 5. This mishnah deals with a situation in which the husband is not available to issue a warning of kinui to his wife, and yet a warning is needed, because she is behaving in a way that does not accord with the standards of modesty. In such a case beis din steps in and issues the warning in his place.
"V'eilu shebeis din mekanin lahen" - and these are the women to whom beis din issues the warning of kinui:
"Mi shenischaresh ba'alah" - a woman whose husband became deaf, so that he may not be aware of what is going on around him and is unable to issue the warning.
"O nishtateh" - or whose husband lost his mental competence, so that he is not of sound mind to warn her.
"O shehayah chavush b'veis ha'asurin" - or whose husband was locked up in prison, so that he cannot carry out the kinui.
Since in these situations the husband is prevented from issuing the warning, the Sages said that beis din issues it in his place whenever she needs to be warned.
For what purpose is this kinui carried out?
When the Sages stated this law, they did not state it so that she should drink the water: "Lo l'hashkosah amru ela l'foslah miksubasah" - they did not say this in order to have her drink, but only to disqualify her from her kesubah. Having her drink is not possible here, since the verse establishes that it is the husband who brings his wife, and since the husband is not present, this cannot be fulfilled. The purpose of the kinui, then, is to disqualify her from her kesubah if she acts against the warning and secludes herself with that man.
The view of Rabbi Yose:
"Rabbi Yose omer: af l'hashkosah" - Rabbi Yose says that the kinui of beis din is relevant to having her drink as well. In what way? It depends on the return of the husband, whom she requires: "Lichsheyeitzei ba'alah mibeis ha'asurin - yashkenah" - when her husband is released from prison, he has her drink. That is, once the husband leaves prison he can have her drink on the strength of the kinui issued by beis din, if she violated the warning and secluded herself with the man about whom she was warned.
In summary: We have learned that in three situations in which the husband cannot issue a kinui - he became deaf, he lost his mental competence, or he was locked up in prison - beis din issues the warning to the woman in his place. According to the Sages the kinui does not take effect regarding having her drink, since the verse requires that the man bring his wife, but it does take effect to disqualify her from her kesubah if she violates the warning and secludes herself. According to Rabbi Yose the kinui takes effect for having her drink as well, when the husband is released from prison and has her drink on the strength of the kinui of beis din.