the waste after perfect ignition is CO2 and H2O
so water comes when the out side temperature is colder and steam coming out of the exhaust condenses and becomes water.
These are sign of a good engine but not all the time..
many weaker engine also do the same in the morning because at the start and for few mins normally cars are running @ 1 or 2 RPM max.
weaker engine shows its symptons at higher RPM