The fitness helps, as does the alertness, always looking and paying attention. You are guarding lives, so that moves on to guarding the ball, knowing where the ball is and how to read the game.
Troy Armstrong is a vital cog in Green Bay High's premier boys' water polo side as it tries to foot it with the sport's Auckland heavyweights.
A fast swimmer with a strong arm, the 16-year-old Year 12 student leads Green Bay from the front as captain. He is in the New Zealand Under 17 squad that is aiming to compete in the junior world championships in Montenegro next year, and plays senior club water polo for Waitakere.
Armstrong hones his fitness in summer as a Piha surf lifesaver.
"The fitness helps, as does the alertness, always looking and paying attention," he said. "You are guarding lives, so that moves on to guarding the ball, knowing where the ball is and how to read the game."
Armstrong is an outside shooter and 2m attacker, so he features frequently on the scoresheets.
Green Bay coach Chris Beaumont is someone for whom he has the utmost respect, and the two are Waitakere senior clubmates.
The renaissance of Green Bay water polo started in 2013, when the junior boys' team, of which Armstrong was MVP, won a bronze medal at the North Island Schools championships.
Many of that side have graduated to the premier ranks after playing well in the Senior Bs last year, paving the way for promotion.
Armstrong says the three or four Year 11s in the side are "really pulling their weight" as Green Bay contemplates a 1-1-1 record in their opening three games, beating the second Auckland Grammar team.
But bigger challenges lie ahead, starting with Westlake this Friday night, then going on to defending champions Sacred Heart.
"It's a massive leap," Armstrong said. "In Senior B, you get the odd good player, but the premier grade has speed, intensity and strength and you have to see if you have what it takes to finish off mentality-wise.
"This team has a lot of potential, they have a lot of responsibility as well, but I think they can pull through for what we want to achieve, which is ideally top six in the country. The ultimate goal, though, will be winning the bronze medal at the nationals."
Those senior schools nationals are in Wellington in April, preceded a fortnight earlier by the North Island championships in Auckland.
Armstrong is gearing up for a huge water polo year. He had to juggle plenty with NCEA last year - playing U16s, 18s, and 20s for his club as well as school and senior club water polo. There is more on his plate this year, with more training, higher recognition and school studies.
Life for him is largely a triangular route between his Titirangi home, Green Bay High and the pools at West Wave. But he is enjoying the challenges and the pressure of captaincy and he would love to go far in water polo.
"I'm going to stay in the sport for as long as I can. Playing for my country would be great, but playing for a European club is probably the ultimate goal. That's where I can make a career out of what I do, which would be really good."
Green Bay is fielding four water polo teams; in the premiers, senior Bs, and juniors in the boys' competition, and a senior Bs girls side.