Boot said Zephyr's friend's father came around and at that stage Zephyr's friend was convinced he had drowned.
"It was horrible. All the family gathered at our house on [Saturday] night and we just sat around waiting for the news.
"We still felt hopeful. We kept that hope alive but of course it was harrowing even so."
Despite feeling hopeful, the news at 7amthat their son was alive and well was naturally "incredibly relieving".
Boot said Zephyr and his friend were quite experienced kayakers and had come up to the North Island with a list of rivers they wanted to kayak, which including the Kaituna River.
Zephyr has outdoor experience, had done outdoor education in high school and has friends who are kayakers too.
"He's a level-headed thinker most of the time anyway."
Boot said Zephyr had got himself out of the river and tried to climb out of Gnarly Gorge about 2pm on Saturday.
When he wasn't able to, he secured himself to a tree in case he fell asleep, and covered himself up with leaves, keeping active to keep warm while waiting for searchers.
Boot said he had also cut the arms off his polypropylene top and put them over his feet as he had lost his kayaking shoes.
"We were just very relieved and proud of his resilience.
"He's in good spirits now and not really any worse for wear. He's very tired."
Police praised the teenager, saying he did all the right things when he found himself in trouble in the water.
Senior Constable Colin Fraser, of police Search and Rescue, said Okere Falls Volunteer Fire Crew and Rotorua Rafting helped with the search and rescue.
Fraser said the teenagers had been well prepared for what they were doing, having the right kayaks and wetsuits.
Rotorua Rafting owner Sam Sutton, who is also part of the Okere Falls Fire Brigade, said finding Zephyr was "quite the relief".
"I guess it goes through your head that you could be doing body recovery, but fortunately we didn't have to do that."
Sutton said Zephyr had done a great job staying put and waiting until the morning.
He said the teenager would have had 16 hours waiting in the same position, stuck on a ledge until the river receded.
Members of the public on the Rotorua Daily Post Facebook page were also quick to praise the teenage kayaker's wise decisions around his personal safety.