The study found about 65,000 of 1.5 million properties in prime areas of greater Melbourne could be left empty at time when more than 22,000 Victorians are believed to be homeless.

These homes either used no water at all, or less than 50 litres a day over 12 months. A leaky tap is estimated to use up to 55 litres of water a day, according to the report.

The seventh annual Speculative Vacancies study was commissioned by tax-reform group Prosper Australia, which blames the glut in unused homes on investors who hoard properties for long-term profit.

Because these homes are not listed for rent, they say this data is not included in official short-term vacancy rates, which currently sits at 3.1 per cent in Melbourne.

Prosper Australia project director Karl Fitzgerald said, based on the water data, Melbourne's actual vacancy rate was closer to 7 per cent.

The urban-renewal suburb of Docklands had the highest number of speculative vacancies, with 489 or 17 per cent consuming no water Iin 2013. Another 290 used less than 50 litres of water on average each day, leading to assumptions that they were empty or rarely used.

With thousands more apartments planned for Docklands in the next five years, the report said the new developments risked "being dubbed 'ghost towers' should there be a marked decline in economic activity".

Savills national head of research Tony Crabb believes a more likely explanation for current collection of empty homes was travelling retirees and home buyers that were not yet ready to move in.

However Mr Crabb warned that the vacancy rates would climb in the future if overseas investors were to buy up the majority stake in apartment towers. Some of these foreign buyers may not consider it worthwhile to rent out their Melbourne properties, he said.

"Sometimes it might be more trouble than it's worth," he said. "There is no doubt the vacancy rates will jump in the coming years."

Hong Kong is already dealing with a property-hoarding problem, blamed on mainland Chinese investors.

Mr Crabb said Melbourne City Council should implement substantially higher rates for unoccupied properties. "Basically hurt money," he said.

Melbourne City Council recently found 85 per cent of apartments in the municipality were purchased by investors as a "financial product", while nationally,  investor housing loans now account for about half of all housing loans (excluding owner-occupier refinancing).

Other inner-city suburbs experiencing high vacancy rates are Carlton South, West Melbourne and Abbotsford. In the outer south eastern suburbs, 12.4 per cent of Cardinia and Clyde homes reported no water use.

Prosper Australia are calling for the stamp duty paid on new homes to be replaced with a holding cost on land, making it less attractive for investors to keep empty properties.

Mr Fitzgerald said capital gains of $60,000, for example, were so lucrative that renting out a property for $17,000 was a lower priority for some investors.

"Not all investors do this but the super wealthy ones probably understand that if they left 10 to 20 per cent of their portfolio empty it enforces scarcity and pushes up rent and property prices," he said.

Prosper Australia is holding a public presentation about its report on Wednesday.