Some quick research has provided me with this fascinating insite into the stench or urine and poissible causes that unrelated to the act of passing urine on said stenching area:
"At the 100th General Meeting of the American Society for Microbiology in May of 2000, a study was presented that pointed to microbiological degradation as the cause for stinky carpet.
In lay terms, tiny microorganisms (bacteria) find a home in the latex backing of the carpet, and during their growth produce butyric acid, which is a weak acid that will not harm the carpet, but does have a decided odor that to some humans (and cats apparently) smells like cat urine. This particular bacteria appears to be anaerobic, which means it is capable of growth outside of oxygen. The standard disinfectant used in carpet manufacturing apparently does not affect these microorganisms, and any new disinfectants will need to be tested to ensure they do not harm the latex backing"
Therefore, one must not jump to the conclusion that a pet or loved one has "passed water" in the offending area.
More on this article can be found
here