Rashi says that the Kiyor was for water that was given to a woman suspected by her husband, and it was a tool for making peace between husband and wife. You can look at it another way; i.e., it was there to “catch” a wicked woman and to kill her, since those waters were: מ ַי ַםַַה מְא ַר ר יםַ curse-bearing waters and were dangerous to a guilty woman. Only for the innocent woman it remained a medium to bring peace; when a husband saw that his wife had not sinned, since the water only killed when guilty.
Yet, the Kiyor is called an instrument for peace. Notice how the Torah speaks positively. Similarly, we have the Mitzva of: ק ַידוּשַַַי ד ַי ַםַוְַר ַגְַל ַי ַםַ (for a Cohen to wash his hands and feet before doing the Avoda) and the Torah says you’ll wash your hands and you won’t die, and we derive from there the opposite, that there is a punishment if you don’t wash. Yet, the Torah speaks only positively. And the same with many Mitzvos of the Bais Hamikdash, it says: וְלֹאַי מוּת he will not die.
The Gemara in Brachos speaks about how Dovid remarked how he was busy dirtying his hands with all kinds of discharges: לְט הֵרַא ש הַלְב עְל הַּ in order to Paskin that she is Tahor. Actually, she could be Tamei or Tahor; yet Dovid calls his job: לְט הֵרַא ש הַלְב עְל הַּ “I’m here to make pure.” Look how the Torah always speaks positively. When a person has a job with a happy side and a difficult side, he should say: “I’m going to have my fun.”
