Three young British tourists who died after falling down a waterfall in Vietnam during a water-sliding ride were not properly warned of the dangers involved, a coroner has ruled.

Sisters Izzy Squire, 19, and Beth Anderson, 24, died with their friend Christian Sloan, 25, at the Datanla waterfalls in Lam Dong province in Vietnam’s Central Highlands in February 2016.

The women, who were from the Ecclesall area of Sheffield, were seven weeks into a backpacking tour of Asia when they died. Their father, David Squire, has described their deaths as being “wholly preventable”.

The coroner Chris Dorries heard how the friends wore life jackets and helmets as they slid head-first down a natural water slide before ending up in a 2-metre-deep pool. Instead of leaving the pool, the trio were swept along by strong currents and disappeared over the next tier of the river complex, dying when they were then thrown down a 15-metre waterfall.

Their guide, Dang Van Si, claimed that he told them how to get out of the pool safely. However, this was contradicted by a range of witnesses who were found through a Facebook appeal by Sloan’s family. The coroner ruled that either Si did not give any warning to the backpackers or he did not make sure it was properly understood.

Dorries told Sheffield coroner’s court that, contrary to the reports at the time, the travellers had done nothing to compromise their safety. “They had chosen the tour with care,” he said, pointing out that the tour had been booked through a recognised agency and that Anderson had been reassured it was not an excessively adventurous activity.

“They were not adequately warned of the risks to be found at the bottom of the slide,” he continued, “and, in particular, that there was a potentially lethal hazard of a further waterfall which they could be swept in from only 14 metres further on.”

He told the court: “I was disturbed to hear from the families that, in the period following the deaths, the uninformed chose to make a number of allegations that the trio acted unwisely. That may not be a sufficiently forceful word. Let me be clear from the outset, there is no evidence at all that such was the case.”

Families of the sisters and Sloan attended the inquest. Speaking outside the Medico-Legal Centre in Sheffield, David Squire said: “It’s now been confirmed what we, as families, have known all along. Christian, Beth and Izzy were completely innocent and lost their lives through no fault of their own. Instead, a series of individual failings and persistent breaches of Vietnamese laws and regulations led to our children’s untimely deaths.”

Squire said that the communication between the Foreign Office and the Vietnamese authorities “leaves a lot to be desired”, so he did not know how the criminal investigation into the deaths was progressing in Vietnam.

“Part of our hearts and souls and our very being died with Beth and Izzy on that inexplicably awful February Friday,” he said. “They will be for ever just 19 and 24 and for ever young.”