After 11 hours and no sign of rescuers, the couple and eight others decided to swim to an island.
"We quickly got split into small groups in quite big seas," said Ms Wilkinson.
"The Flores Sea is notorious for strong currents and big seas, but we all made it."
After six to eight hours, they reached land - an active volcano with no fresh water.
"We all landed in different places on the island. Nobody lives there because it is an active volcano ... still spitting hot lava and smoking all night."
But they were on dry land after 18 hours in the water. "Thank heavens we all had life jackets."
Five of the group were picked up by a passing fisherman, and the others - who were further north - were picked up by a dive boat.
"They looked after us so well," Ms Wilkinson said.
"We are all fine - nobody with hypothermia, just quite badly burnt from being on the water in hot sun for so long. Tony's face and eyes are really sore, but we are alive."
The couple, who live in Takaka, at the southeastern end of Golden Bay, are both search and rescue volunteers and were on the ferry with 18 other foreign tourists, a local guide and four crew.
Ms Wilkinson also spoke to 3News about drinking urine: "When we arrived on shore, we'd already been in the water for 18 hours and we just needed a drink, so you do what you do."
Mr Lawton told the Associated Press agency that he believed the ferry hit a coral reef the day it left Lombok.
"It then floated off at high tide, so maybe then that was the cause for the boat to sink - we don't know."
Pema Parigot, who is house-sitting the couple's South Island home, said both her friends were "very, very fit", which would have helped their survival efforts.
"I think that would have saved them. They're okay. It was one hell of an ordeal. They're coming home."
The couple were four weeks into a six-week "outdoors holiday", Ms Parigot said.
"They're into the whole works - the whole outdoors activity [scene]. Both of them are search-and-rescue [volunteers] so that would have helped the ability to survive."
Ms Wilkinson's mother, Ngaire, who lives in Nelson, said her daughter was a swimming instructor and had taught outdoor education for 20 years.
She ended her teaching career last year when she retired from Golden Bay High School.
"They're both very active sports people. They're going to come back shortly, I think. They're pretty strung out."
The couple, who enjoyed travelling, had been in Bali and were also on a diving course as part of their holiday.
"They were going up the islands."
Indonesian officials yesterday said rescuers had picked up 13 more people from the doomed ferry trip, but a man from the Netherlands and a woman from Italy were still missing.
A boat trip from Lombok to Komodo, home of the Komodo Dragon, can take up to 15 hours.