Parah, Chapter 9, Mishnah 9. This chapter traces the various ways in which mei chatas, the water prepared with the ashes of the parah adumah, can be ruined, and asks what tumah the ruined mixture still carries. Our mishnah presents a case in which the ashes were perfectly fit, but the water beneath them was not.
The mishnah opens with "eifer kasher shenasano", fit ashes that a man placed, "al gabei hamayim", onto water, "she'einan re'uyin lekadesh", water unsuitable for the act of kiddush. Of such a mixture the mishnah rules: "metam'in es hatahor litrumah", it conveys tumah to one whose taharah reaches only the standard of terumah, and this happens "beyadav uvegufo", whether the contact was with his hands or with his body. As for "es hatahor lechatas", one who stands at the taharah demanded for chatas, the ruling is "lo beyadav velo vegufo": no tumah reaches him through his hands and none through his body.
The principle behind the ruling
Sanctifying the water demands water suited to that use, and here the ashes were joined to water that could not serve, so nothing usable for sprinkling was produced. Yet invalidity does not cancel the tumah inherent in mei chatas. Genuine mei chatas transmits tumah upon touching a human being or a utensil, even in an amount smaller than what sprinkling requires, while it leaves entirely untouched anyone who maintains the taharah that chatas demands. Water that has been rendered invalid keeps precisely that same profile.
The two people in the mishnah
A man who is tahor only to the degree required for terumah is therefore rendered tamei by this mixture, whether it reached his hands or came into contact with his body, and he in turn renders terumah tamei.
A man who is tahor at the level required for chatas, by contrast, is entirely unaffected. Neither contact with his hands nor contact with his body renders him tamei.
The lesson of the mishnah is that a flaw in the preparation of mei chatas removes its fitness for sprinkling while leaving its tumah fully in force, and that the higher taharah of chatas remains a complete shield against it.