Now at just 19, he is an apprentice electrician who works part-time for Laser Electrical Hastings, all while juggling up to 22 hours of swimming and gym a week.
Late nights and early mornings are not new for the athlete, who attends up to 11 two-hour trainings a week, with some starting at 5.30 in the morning.
At 7 years of age he started winning age group titles and at 9 was ranked No 1 going into National Age Group Swimming Championships in the 50-metre backstroke.
At 11, with trophies and medals under his belt, he decided he had enough of swimming and gave it up. However, at 16 he approached his former club, the Sun Devils, based in Flaxmere, and within a year started to shine again.
In 2016 he won his first age-group title in the 50m freestyle and was a member of the bronze-winning club relay team.
His success continued into 2017. He has turned down opportunities to train with top clubs in other regions. Joshua believes he can reach the pinnacle of his sport from his home town: Flaxmere.
"I just think I've got enough support here and the right things to get to the next step. I don't need to move away."
This year, he hopes to get on the New Zealand team and get a medal in the open age groups, as well as sticking to his trade.