Pesachim 17 - The impurity of liquids
The Torah described the ritual impurity of foods. It also says that foods can become impure only after they were made wet with a liquid. This leaves us with a question: can liquids themselves become impure?
We can start with one fact that is certain: Rabbi Yosef ben Yoezer testified that the liquids in the Temple are pure. However, there are different ways to understand his words. For example, Rav understood them literally: these liquids are totally pure; Shmuel, by contrast, said that they are pure only in the sense that they don’t transmit impurity to other things, but they themselves can become ritually impure.
Rav explains that the Torah laws of impurity do not apply to liquids. The Sages extended them to liquids for people to be more careful, but stopped short of making the liquids in the Temple impure, because the Kohanim are careful anyway. Shmuel explains that on the contrary the Torah laws of impurity do apply to liquids - but only to themselves, not to transmit impurity to others. The Sages extended the laws of impurity further, giving liquids the power to contaminate other foods, but stopped from accepting these laws in the Temple.
There are different versions of the testimony of Rabbi Yosef: some say it applied to the place of washing the sacrifices only, while others - that he meant anywhere in the Temple. Rav Pappa complicated this even further, saying that the laws of liquids in the Temple were told by God to Moses as an exception, and thus no conclusions can be drawn from them to other areas of life.
Art: Washing Day by Edward Stott