Is washing a spot of doubtful impurity – where water transfers from front to back, and it is presumed to be impure, then the spot it reached is washed, then the hand, then the spot that water is predominantly thought to have reached – considered a waste of money that necessitates compensation?

The questioner is advised to ignore excessive obsessive thoughts (waswas). It is sufficient to wash the area of impurity until it is highly probable that the impurity has been removed. There is no need to meticulously trace the areas where water used for istinja' (washing after defecation/urination) has spread, as this water is pure unless it has changed due to impurity. There is no need to wash an area if one doubts its impurity, because the original state is purity, and impurity is only declared with certainty. What happened is not considered a waste of money. The religion of Allah is ease, and one must struggle against obsessive thoughts.