An analysis of Taswater data suggests up to 2,000 homes could be sitting empty across Tasmania, despite Hobart having the tightest rental market in the country.
The Tenants' Union used water consumption data to estimate how many empty houses there were within three inner-city council areas: Hobart, Launceston and Glenorchy.
If a property used less than 10 per cent of its annual average water consumption over three consecutive years, it was deemed empty.
"It's extremely disheartening that we have up to 2,000 empty homes across Tasmania during a housing crisis," Ben Bartl from the Tenants Union of Tasmania said.
"Not shacks. Not Airbnbs. Just empty."
Amelia Spence, 20, is living in a homeless shelter and says it is hard to hear about homes being left empty when so many people are looking for a rental.
"At the moment I am homeless … because I haven't been able to find a rental since my last share house fell through," she said.
She said that government plans to build more social and affordable homes would come too late for many.
"I feel like we can't wait three years. There are people that need housing now," she said.
Despite working part-time — about 28 hours a week and earning about $500 a week — she has struggled to find a place to rent.
Ms Spence said the few rentals she could afford received multiple applications.
"Even though I apply, I just don't hear back from them," Ms Spence said.
"It's scary because I don't really feel like I have much hope of finding a place at the moment."
For the past 11 weeks, Ms Spence has been living in homeless shelters.
"I can stay at the one I am at for another two months and, possibly, renew that for another three months after that if I still haven't found a place," she said.
"But it's still not a home, it's only somewhere where we can't sleep overnight. We can't stay during the day."
Ms Spence would like to return to university part time but said she could not make any plans without a place to live.
People 'sitting on' investment properties, union says
The data found there were 192 vacant residential properties in the Hobart City Council area, 115 in the Glenorchy municipality and 256 in Launceston.
When reviewing the data, the Tenants Union excluded areas with a high number of shacks, and calculated that, across Tasmania, there could be between 1,486 and 1,932 empty homes.
"That is, homes that are just sitting there while we have a housing crisis," Mr Bartl said.
"There are thousands of people looking for affordable rental properties.
Hobart has the lowest rental vacancy rate of any Australian capital, at 0.9 per cent.
Launceston's vacancy rate is 0.8 per cent.
Calls to introduce 'empty house' tax
Mr Bartl wants the state government to introduce an empty home tax to act as disincentive to investors.
"In Vancouver and Melbourne, if you leave your home empty for more than six months without a reasonable excuse, you are charged 1 per cent of the value of the property."
He said the revenue could be invested in affordable housing.
"With the average house price in Hobart $675,000 and in Launceston $461,000, a 1 per cent tax on empty homes in the Launceston, Hobart and Glenorchy municipalities would have raised $3.2 million for affordable housing each year, or almost $10 million for affordable housing over the past three years."
Mr Bartl argues it would also put downward pressure on rents.
The Rental Affordability Index found Hobart was the least-affordable capital city in Australia.
Matt Haubrick from the Housing Alliance Tasmania supports the idea.
"It's a bit of a disgrace," he said.
"The majority of people are just having to stay living at home, living with friends, living on couches, living in lounge rooms or in their vehicles.
"Those are the lucky people who have some sort of support network and aren't forced to live on the streets or in crisis accommodation."
Government rules out disincentives
The Minister for Housing, Michael Ferguson, ruled out imposing an empty house tax.
"Without clarification on what is captured in their statistics regarding vacant lots, houses under construction or in the planning phase or other factors that might result in low water usage, it is very difficult to say how relevant the statistics provided by the Tenant's Union are," he said.
He said the government's priority was addressing housing supply issues.
"This is the only way to combat the rising housing [prices] and put downwards pressure on home prices and rentals," Mr Ferguson said.
The Tasmanian government plans to build 3,500 new social and affordable houses by 2027.
