George and Shelley Pashby thought an underground pipe had burst when water began gushing into their garden in Plymouth, Devon.
But tests have found the steady stream of water, which appears to be spilling from beneath the house, is not the result of a burst main.
Although there are known natural springs in the area, water officials said it was not yet known as to why one has suddenly appeared.
The most likely theories were that the water has come up from an old well, or from a spring source covered up by urban development.
Mrs Pashby said her family had lived in the house for 10 years and had never had such a problem.
"It is a mystery", she said. "The structural engineer who came up here said it is definitely springs."
Mrs Pashby, 30, who has four children, Jade, 11, George, nine, Billy, three, and five-month-old Jack, said the family was now seeking to move out.
The discovery has led to suggestions that the family could bottle and sell the water, echoing the plot of the BBC sitcom Only Fools and Horses in which brothers Del Boy and Rodney Trotter sell 'Peckham Water' from their home.
However sources at South West Water said they believed it would be impossible to do so because the property was owned by the council who would almost certainly have any mineral extraction rights. Strict health regulations would also govern the process, the sources added.
A spokesman for Plymouth City Council said: "We have been doing everything we can to identify the source of this problem.
"If there is no fault with the main then this would suggest an underground spring or blocked culvert may be causing the problem in which case we would have to take appropriate action to divert the water."
"We have employed a firm of geological consultants who are carrying out detailed investigations, including looking at local structural plans of the area. These investigations will take some time to complete."
South West Water said it would visit the property to take water samples for testing, which would enable it to establish its source.
