Tractate Mikvaot - Chapter 1 - Mishnah 6 מקוואות פרק א׳ משנה ו׳

Superior to such [water] is the water of rain flows which have not stopped. If an unclean person drank of it and then a clean person drank of it, he is clean. If an unclean person drank of it and water was then drawn from it in a clean vessel, it is clean. If an unclean person drank of it and a loaf of terumah fell in, even if he washed his hand in it, it is clean. If one drew water from it in an unclean vessel and then a clean person drank [out of the pool], he is clean. If one drew water from it in an unclean vessel and a loaf of terumah fell [into the pool], even if he washed his hands in it, it is clean. If unclean water fell into it and a clean person drank of it, he is clean. If unclean water fell into it and one drew water from it in a clean vessel, it is clean. If unclean water fell into it and a loaf of terumah fell in, even if he washed his hands in it, it is clean. [All such water] is valid for terumah and for the washing of the hands.