Makshirin, Chapter One, Mishnah One
1) Any liquid which was desired at the beginning though it was not desired at the end, or which was desired at the end though it was not desired at the beginning, comes under the law of “if water be put.”
2) Unclean liquids render unclean whether [their action] is desired or is not desired.
Section one: For a liquid to make produce susceptible to impurity its contact with the produce has to be desired either at the beginning or the end. The “beginning” is when the liquid came into being, or was separated from its natural source. Rainfall begins when it comes from the sky. If while the rain is falling a person says or thinks to himself that he wants to use the water for some purpose, then the rain is “desired.” Alternatively, if he is happy that the rain fell on his produce, then the rain is desired.
“Not desired at the end” means that too much rain fell on his produce.
If it was desired at the end but not in the beginning means that at first he was not happy with the fact that water was falling on his produce. But then, at the end, he saw that this was good and he was happy. All’s well that ends well, as they say.
In either case, the produce is susceptible to impurity. It would only not be susceptible if he was never happy that it got on his produce.
Section two: Unclean liquids, those that have already been defiled in some way, make produce susceptible whether or not their contact is desired.