Makhshirin, Chapter Four, Mishnah Three
1) If one inclined a dish against a wall that it might be rinsed [by rainwater], it comes under the law of if water be put.
2) But if in order that the wall might not be damaged, it does not come under the law of if water be put.
Section one: Again, the whole issue here is intent, as it is generally in these mishnayot. If he intended for the dish to get rinsed off, then the water does cause susceptibility.
Section two: But if he only put the dish up against the wall so that it would protect the wall, then the water has not been “used” so it doesn’t cause susceptibility.