Brown became ill while swim training ahead of a senior men's session on Thursday, NHWP said in a statement on Facebook yesterday morning. He later died.
A gathering was held in his memory at the Finish Line at AUT Millennium at 4pm with hundreds of people attending to pay their respects.
Rowan Brown
We are devastated to announce the death last night of Rowan Brown - one of our most talented and hard...
Posted by North Harbour Water Polo Club on Thursday, January 23, 2020
It was a "lovely gathering", Watson said, with Brown's parents in attendance and the pool where he fell ill was also blessed.
"The room was as quiet as anything and there was a lot of sadness but it was important to be together," she said.
In their Facebook post, NHWP said Brown was a vital member of the senior men's team and was a "true inspiration" to others.
"Our hearts are breaking for Rowan's wonderful family, Megan, Stan, Jordan and Caiden," they wrote.
"Rowan was a familiar face to so many of us around the pool not only as a Rangitoto, NHWPC and NZ player but also as a passionate coach and mentor to so many in our club."
Many commenters on the post agreed, with many passing on their condolences to the family of the young man.
Brown represented New Zealand's national water polo team on debut at the FINA World Championships in South Korea last year.
But he was not only a strong performer in the pool, he was also a "really talented" coach and mentor, Watson said.
Many people were still "in extreme shock and sadness" after the young man's death, Watson said.
"He leaves a massive hole in many groups, teams, communities ... it's only been a few days and no one has really begun to process it properly," she said.
"I think it's important to stress what a wonderful young man he was personally - he was kind and respectful to all age groups.
"He was quite exceptional on his outlook on life, his happiness, his consideration of others, his love for his family and friends, he was truly exceptional."
A farewell service for Brown would be held on Wednesday at 4pm at the Rangitoto College Auditorium, a post on the NHWP Facebook page said.
The family reportedly asked for people to wear loud and colourful shirts, as they were what Brown loved to wear.