Parah, Chapter 9, Mishnah 8. This chapter follows the fate of mei chatas, the spring water into which the ashes of the parah adumah were placed, when something goes wrong with it. Our mishnah takes up two separate mishaps and asks the same question about each one: whom does this water still render tamei? It draws a sharp line between a person who is tahor at the level required for terumah and a person who is tahor at the higher level required for chatas.
The first case opens with water that has gone unfit: "Mei chatas shenifsilu", chatas water that became disqualified. Such water, the mishnah rules, "metam'im es hatahor litrumah", transmits tumah to a man whose purity reaches only the standard demanded for terumah, and it does so "beyadav uvegufo", whether the contact is made with his hands or with any other part of him. But as for the man who has attained the stricter taharah of chatas, "v'es hatahor lechatas", this water leaves him wholly unaffected: "lo beyadav velo vegufo", not by way of his hands and not by way of his body.
The second case turns on a single word, "Nitm'u": the water itself contracted tumah. Here too the ruling is that it "metam'im es hatahor litrumah", contaminates the man whose purity extends only to the level of terumah, "beyadav uvegufo", through contact with his hands and equally through contact with his body. With regard to the man who is tahor for chatas, however, the ruling now divides: "v'es hatahor lechatas beyadav", his hands are affected, "aval lo vegufo", while his body is not.
The background rule
Some background is needed first. Water of chatas that has been sanctified with the ashes transmits tumah upon contact even in a quantity too small to serve for sprinkling, and it does so both to human beings and to utensils. Yet someone whose state of purity meets the standard that chatas demands suffers nothing from this water at all: it defiles him neither when he touches it nor when he carries it.
The scope of that immunity is disputed. According to the Rambam it operates only while the man is engaged in the sprinkling procedure itself; if he takes hold of the water or transports it for any other reason, unrelated to the haza'ah, he does become tamei. The Rosh offers no such qualification: a man who is tahor for chatas is unharmed by the water even when his touching or carrying serves no purpose bound up with sprinkling. In another place, however, the Rosh implies that such taharah functions only within the domain of chatas itself, meaning that the man may still draw the water, sanctify it and sprinkle it, while for everything else he is reckoned tamei. The Gra rules like the Rosh and formulates the principle in the widest terms: mei chatas defiles only a person who is tamei as far as chatas is concerned, and never one who is tahor for chatas.
Water that was disqualified
With that in hand, the first clause of our mishnah becomes clear. Mei chatas that was rendered unfit does not thereby lose its power to convey tumah; it carries exactly the same status as valid mei chatas. Accordingly, a man who is tahor only at the level of terumah is rendered tamei by it whether he touches it with his hands or with any other part of his body, while a man who is tahor for chatas is untouched by it entirely.
Water that became tamei
The second clause deals with water that itself contracted tumah, and here the halachah shifts. Such water now falls under the general law of tamei liquids, and tamei liquids render the hands tamei. Therefore even a man who is tahor for chatas has his hands rendered tamei by contact with it; and in the realm of chatas, once a man's hands are tamei his whole body is treated as tamei. Contact with his body, however, leaves him tahor, since impure liquids do not convey tumah to the body itself through touch. The one who is tahor merely for terumah, of course, is rendered tamei either way.
The mishnah thus teaches two lessons at once: disqualification does not diminish the tumah of mei chatas, while tumah in the water introduces a new and different form of contamination, one that reaches even the hands of a man who is tahor for chatas.