Makhshirin, Chapter Five, Mishnah Three
1) Produce onto which a leak [from a roof] fell and he mixed it up in order that it might become dry [quickly]:
a) Rabbi Shimon says: it comes under the law of if water be put.
b) But the sages say: it does not come under the law of if water be put.
The water from the leaky roof itself doesn’t make the produce susceptible to impurity because he didnt want it there. However, according to Rabbi Shimon, if he mixed the produce up so that the water would be absorbed into it, the produce is susceptible. Although he didn’t originally want the produce to get wet, he did want the water to be absorbed into it. This is sufficient intent for the produce to be susceptible.
The other sages say that since he didn’t want the produce to get wet in the first place, it is not susceptible.