With water restrictions affecting most Australian capitals, more than 35 per cent of houses in most states were experiencing cracking as the ground dried out, an Archicentre survey of 75,000 homes around the country has found.

"When the soil dries out, strain is put on the house structure and cracks can appear overnight," Archicentre general manager David Hallett said.

Returning moisture to the soil could allow cracks up to five millimetres wide in brick walls to close up, Mr Hallett said.

"We may see people with cracks in their homes strategically watering their homes with buckets of water recycled from the shower," he said.

According to the research, South Australia was the worst affected state, with 48 per cent of surveyed houses affected by cracking.

In Tasmania, 45 per cent of homes were affected, 38 per cent in Victoria, 36 per cent in NSW and WA, and 18 per cent in Queensland.

Mr Hallett said homeowners should not panic if they saw cracks in their house but should monitor them and seek professional advice before undertaking major structural work.

Archicentre expected a rise of 10 to 15 per cent in the number of Melbourne houses developing cracks if the city moves to stage four water restrictions in April, as expected, Mr Hallett said.

While the age of houses and local soil types also played a part in causing cracks, Mr Hallett said the effects of the drought on houses were obvious.

"As the soil dries out, a lot of people will see it contracting away from the house, and it's after that you'll see cracks appearing," he said.

"I think we're not far from the time when people have to not only collect their shower water or rainwater, or whatever they can, but they'll also have to start making decisions about where to use it.

"If your choice is your house or your prize hydrangeas, perhaps the house needs to take precedence."

In Melbourne ageing inner-northern suburbs lead the list of biggest cracks, with 75 per cent of North Carlton homes showing signs of cracks.

Nearby Fitzroy, Carlton and Collingwood were close behind, but Mr Hallett said the dry would affect houses across Melbourne.

"I think the increase in cracks will be pretty consistent all over the place," he said.

While cracked foundations can cost home-owners up to $50,000 to fix, Mr Hallett said smaller cracks could be fixed with rainwater.

"Ideally, people should be storing rainwater in a tank, and have a drip irrigation system around the perimeter of a home," he said.

But saving walls was not as simple as pouring on the litres.

"Too much water can do as much damage as too little, and a sudden influx of litres does more harm than good," he said.

"But a slow-drip system gradually rehydrating the house is a good idea."

With the Herald-Sun and AAP

www.news.com.au/story/0,23599,21037434-421,00.html