The Englishman found the net twice in the first half at Vicarage Road to take his league tally to 19 this season, helping Pep Guardiola's men to a convincing 4-0 victory.
Sterling blasted in the opener in the 31st minute and ten minutes later, tapped in a second after seeing his penalty saved by Ben Foster.
With one league match remaining, the winger is hungry to take his tally to 20.
"It's massive as a winger to score 20 goals in the Premier League," he said. "It's a massive achievement and we have one more game left, so I hope I can do it then.
The winger assumed responsibility from the penalty spot, taking over from regular spot-kick specialist Kevin de Bruyne and admitted that he did so with one eye on his number of goals.
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"I scored the first one and I knew I was on 18 so I stepped up. I knew I had another chance to get the hat-trick today, it didn't happen but I'm really happy with the two goals."
City bowed out of the FA Cup last weekend and Sterling believes that the display against the Hornets was the perfect response.
"After a disappointing match at Wembley we had to find rhythm today and we did," he admitted.
Guardiola's side has a UEFA Champions League last-16 second-leg clash with Real Madrid coming up early next month and Sterling feels that putting in good displays now will benefit the team.
"We’ve got to take all we can from these remaining league games and we know Madrid have finished the season well.
"We know it’s going to be a strong test."