I learned to swim almost before I could walk," says Graham Black. "In fact, my mum called me her water baby." That's hardly surprising - as a child in Durban, South Africa, he could not only swim in his family's pool, but also lived a stone's throw from the beach.
Mr Black, 30, has been teaching in the UK since 1994. He is deputy head of science at the all-girls Waldegrave School, Twickenham, one of only half a dozen men among the 55-strong teaching staff. He takes years 7 to 11 through to GCSE.
But there's another side to Graham Black: he is captain of the UK's national lifesaving team.
Competing to save lives might seem odd, but lifesaving is an internationally recognised sport. Mr Black says: "Although competition is secondary to public service, the championships test and develop the skills lifesavers and lifeguards need."
Explaining the distinction, he says lifesavers are members of the public who respond to basic aquatic and medical emergencies, while lifeguards, paid or unpaid, are trained and qualified to supervise and safeguard the public in or around water.
"The world championship contest includes individual and team events. Some heats are held in the surf, some on the beach and some in the swimming pool." The events, one of which is a simulated emergency incident, are based on rescue skills. As well as their fitness and general athletic performance, the competitors' reactions, hazard awareness, and knowledge of first aid and resuscitation skills are put to the test.
Mr Black has a peculiarly personal stake in lifesaving. His father was attacked and badly bitten by a shark. "Most of his thigh muscle stayed in the belly of that shark," he says. "That inspired my brother and me to take up surf lifesaving as kids. In a funny way, we felt an affinity with the sea because part of our dad was in there."
It's a family connection if ever there was one. And it's the same with his career. Graham Black's grandfather was a headteacher, his mother taught in a primary school and his brother is a PE and maths teacher. "It's the job I always knew I'd do," he says.
He trained (and first taught) in South Africa, where his athletic background made physical education his first choice. But that course was fully subscribed. "I sort of got stuck with science," he says. "But now I find it complements my sporting life."
There are conflicts, however. Like the other members of the six-strong men's international squad, Mr Black is an amateur. That means he is largely self-funding; for example, he has to take unpaid leave if he travels abroad during term-time. Luckily, his school is accommodating, although he does his best to avoid interrupting his pupils' coursework.
But Mr Black believes his extramural activities pay dividends in the classroom. "Competing at this level makes me a more rounded person," he says. "I can also draw on my own experiences if the context of a lesson makes it appropriate - for example, explaining the effect of exercise on heart-rate, or how energy is converted into work." And it's a two-way process - Mr Black's academic knowledge of biology, physiology, nutrition and anatomy informs his sporting activities.
"Science helps me understand what I do in training," he says. "I can also pass that knowledge on to my students and to younger members of my lifesaving club." Sport, he maintains, also helps him communicate effectively with his pupils. "The girls ask me about my sporting activities - it gives them more of a handle on me as person, helps break down barriers and counters the stereotypical image of teachers that many pupils have."
Physical training, he says, can release much of the stress of teaching. "It may sound paradoxical, but if I don't train hard before school, I feel more tired during the day. The exertion makes me sharper, physically and mentally. I try to train every day, before and after work."
Mr Black spends much of his time at the track and gym as well as on or in the water. A typical week's training starts on Sunday with a two-hour session at his lifesaving club. Each weekday morning before school, he spends more than an hour swimming in the pool or canoeing on the Thames. After work, he devotes another hour to running, canoeing or swimming. Thursday evening and Saturday afternoon are reserved for his other sporting passion, hockey. It's a gruelling regime - more than 30 hours a week - although Mr Black says it is important not to over-train.
On top of all that, there are the demands of the day job. So how does he fit it all in? "With difficulty," he laughs. "Good time management is vital. I have to be extremely disciplined and organised. I set priorities and deadlines. But the training itself gives me a lot of energy." A social life is important too, so he gives training a miss on Friday and Saturday nights.
With most of his family still living in South Africa, the friends he has made among fellow members of Crawley Town Life Saving Club are important to him. "We socialise a lot. As well as pubbing in London, we go to Devon and Cornwall on surfing trips." He has dual nationality, but does he feel British? "Yes, I do, but I'll never sever my links with South Africa. For example, I was cheering on South Africa against England in the Rugby World Cup.
"But when I'm competing for Britain, I'm 100 per cent committed to my team winning, no matter who the opposition is. If the opponents were South Africa, I wouldn't feel disloyal."
Mr Black is keen to raise awareness of lifesaving and water safety in his school but recognises the limitations of time, money and facilities. "The RLSS's bronze medallion lifesaving award is an excellent scheme for secondary school students. Not only does it give them skills that could save someone in an emergency, it is a rewarding challenge in its own right, promoting a healthy lifestyle and bringing great personal satisfaction."
Unsurprisingly, perhaps, Mr Black believes Britain's education system puts too little emphasis on sport. "There is an enormous reservoir of sporting talent in our schools," he says, "but all too often pupils have to join outside clubs to develop. All schools should be encouraged - and funded - to offer much more. It's not enough for government to rely on the unpaid goodwill of dedicated teachers."
Now at the pinnacle of his sport, Mr Black has represented the UK in home internationals and at European and world levels. He is also active on the national and club scene. Mr and Mrs Black senior must be very proud of their water baby.