Does a person become impure if they step on a carpet that is wet with water, and there is a urine impurity on it, the location of which is unknown?

A foot affected by wetness is pure, and the spot on the prayer rug it touched is doubtfully impure, and certainty is not removed by doubt. If a foot affected by wetness touches an impure place that is not wet, it becomes pure by touching any pure object thereafter.