Machshirin 5:4-5

Machshirin 5:4

If one measures a well – either its depth or its width – Rabbi Tarfon says that ki yutan applies to the water that gets on his measuring tool. Rabbi Akiva says ki yutan applies if he measures the well’s depth but not if he measures its width.

Machshirin 5:5

If a person stuck his hand, foot or a rod into a well to see if there’s water in it, ki yutan doesn’t apply; if to see how much water is in it, then ki yutan does apply. If one throws a stone into a well to see if there’s water in it, ki yutan doesn’t apply to what splashes and the water on the stone doesn’t convey impurity.