Is it sufficient to pour water over the site of impurity after cleaning oneself with the left hand, which has become impure, for fear of the impurity transferring from the hand back to the site?

The best way to cleanse oneself after urinating (istinja') is by wiping with tissues then washing with water. If the left hand becomes soiled during istinja', it can still be used by pouring water over the impure spot and rubbing it until the impurity is removed and the hand and the area become pure. If only pouring water is sufficient, then istinja' with the force of flowing water is enough to remove the impurity, and the basic principle is that it does not spread unless it is known to have done so.