The Saints were denied all three points at Vicarage Road on Saturday afternoon due to a late Abdoulaye Doucoure goal, which was scored via the French midfielder's hand.
In the week that VAR was trialled in English football in FA Cup and League Cup ties, Doucoure's goal looked set to reignite the debate about the need for the technology to be used in the league to prevent similar incidents. "Nothing, only talk about this", said Carvalhal.
Southampton's James Ward Prowse in action with Watford's Richarlison
"This is one of the situations VAR will in the future say "clear penalty" - it will be clear". "My feeling is like the players, we are a little bit sad", he said.
"I think we have to try (VAR) and analyse if it's possible to help the sport to make better decisions, even for the referee".
Deeney produced a target man's master-class after coming on at half-time, rallying his bedraggled teammates and setting up goals for Andre Gray and Doucoure, cancelling out James Ward-Prowse's two first-half goals.
"They'll feel like it's a loss", he said. "If VAR had come in we probably wouldn't get that but today we got it".
How does VAR work?
"My players are conscious we are in a position we have to change, on and off the pitch".
Referees boss Mike Riley has already confirmed changes to VAR will take place for those games, particularly surrounding letting spectators in the stadium know whether the system is being used.