The data also showed a further 1100 properties in the cities were likely to have been empty for two years, and 890 for one year, with a total of 2550 for the council areas of Launceston, Hobart and Glenorchy.

A property was included if its annual water usage was below 10 per cent of the average for one, two or three years - a metric used in other states to determine vacancy rates.

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When asked about the data last week, Housing Minister Michael Ferguson said it was difficult to determine if the data was "relevant" or if it included vacant lots, houses under construction or in the planning phase.

Premier Peter Gutwein described it as a "rough rule of thumb". Both ruled out introducing measures to get these houses onto the rental market.

Tenants' Union of Tasmania principal solicitor Ben Bartl - who obtained the data - went back to TasWater to check if it included vacant lots or under-construction premises.

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"The numbers were done on actual residential premises - that is - ones valued as have a 'Residential Dwelling' actually constructed and habitable by the Office of the Valuer General," the TasWater response reads.

Spot checks carried out by TasWater on various vacant properties also confirmed most had notes on their meters saying they were vacant, or appeared vacant.

Mr Bartl used the data to advocate for a vacant property tax as a way of encouraging owners - including those with multiple investment properties - to put the premises on the rental market, rather than simply leaving them vacant to accumulate value.

Such a scheme exists in inner and middle Melbourne, where owners are charged a 1 per cent tax annually on capital improved value. In the UK, local councils have discretion over the rate of their vacant property taxes.

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Tasmania continues to suffer a housing crisis covering the availability and affordability of the private rental market, a shortage of social and public housing, and overall rapidly increasing cost of housing.

Housing Minister Michael Ferguson said the government already recouped taxes from property owners.

"It's important to note, vacant properties are likely to be already attracting land tax and without rent revenue the land tax would already be having a similar effect as the union's proposed vacancy tax," he said.

"If land tax doesn't motivate a landlord to put a property to the market then a vacancy tax won't either so this is just a cash grab that attempts to punish property owners.

"We will not be taxing ourselves into increased housing, we are boosting supply and already investing huge amounts into housing in Tasmania."

The government has a target of 3500 new social and affordable houses by 2027, along with other incentives to support first home owners and increase supply.

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