The home side came into the match looking for a bounce-back effort after getting drubbed by Tottenham last week, while Swansea were hoping to stop a five-match winless run in league play.
Watford had the better of the play early, but both sides created plenty of chances as the clock struck 42 minutes. The lone goal came then when Capoue found himself in perfect position in the box. His first attempt was blocked, but he stayed with it and fired past Swansea goalkeeper Lukasz Fabianski.
Paul Clement's team didn't lack for character as they continued to push forward looking for a late equaliser, but failed to capitalise on their chances all afternoon. Jordan Ayew and Borja Baston were called upon to add some scoring punch off the bench, but they were largely ineffective.
Still, the Swans had one final quality chance in added time as Baston served a very good ball into the box for a Gylfi Sigurdsson header, but it was off target and flew past the near post as referee Lee Mason blew the final whistle.
The result sees Watford (11-14-7) up to 10th place on 40 points, while Swansea (8-21-4) remain in the bottom three on 28 points.