Westwood, who signed from Crewe for £2million last summer, has settled in impressively into his new surroundings, and has made 23 Premier League appearances since his arrival.
The 20-year-old is now a fixture in Lambert's starting line-up, and will be integral in Villa's efforts to remain in the Premier League. The manager compared Westwood to Paul Scholes in December, and has reiterated his admiration for the youngster's talents.
"I call him that [the water carrier] but it's the biggest compliment I can pay him," Lambert said.
"He's brilliant at it. He does the hardest thing well, which is just keeping the ball.
"The thing is, he never gives the ball away. I know exactly what I'm going to get with him. Coming from where he was and to do what he has done here is absolutely phenomenal.
"Players like Christian Benteke get all the headlines and I suppose a lot of the work Ashley does go unnoticed by some. But not by me. The team functions when he's getting the ball and giving it. He's been great."
Aston Villa face Stoke City on Saturday knowing that a point will be enough to take them out of the relegation zone, at least temporarily.