The robbers also opened the geyser's gas cylinder, allowing gas to leak into the bathroom where the men were being held.
Afrikaans writer Annemari Coetser wrote on her LitNet blog about the attack on her daughter and her family and friends.
Her daughter, Carine van der Westhuizen, said on Wednesday that she and her husband, Pieter, were on holiday with their two children and three other couples and their children.
Staying near Chissibuca
The whole group stayed in two houses at Canda Island near the town Chissibuca. They are all from the Onderberg and Lowveld in Mpumalanga.
"That night at about 19:00 we were getting ready to have supper in the one house. All of a sudden two men burst into the room, armed with a pistol and a teargas pistol, and yelled 'Sleep! Sleep!' I thought it was a joke."
When Carine's husband turned around to lie down, one of the assailants shot him with the teargas pistol.
"My daughter saw how he started to bleed."
The attackers - who were then joined by a third - locked some of the youngest children in one room, some of the women, a man and the teenage children in one bathroom and some of the men in another bathroom.
"They took my husband and I to a room where they tied our hands behind our backs.
"They were very aggressive. The one guy kept saying: 'Money, money'. They were barely able to understand any other English phrases."
At one stage, when the attackers left the room, she and her husband were able to free themselves.
"But when one of them saw us, he kicked me in the face."
That man forced one of the other women to the house next door to look for money.
"He raped her there." Then another assailant tried to rape Carine, but failed.
"They were in no rush - the robbery took more than four hours. They took money and all our electronics as well as all the car keys before they left in a brand new Mitsubishi bakkie."
Carine, whose hands were still tied, then went to the bathroom where the men were and opened the door with her feet.
'Grateful to be alive'
The camp's management called the police, who were about 50km away, and they were at the scene about 90 minutes later.
"They could only speak Portuguese and said: 'We're sorry, missus.'
"You tend to become slack about security measures when you're in Mozambique - open windows and doors and the like. But you're still in Africa and it's still dangerous. We're just grateful to be alive."