David Hallett, General Manager of Archicentre today named the Dandenongs, dotted with cottages and water tanks on old timber stands, as an area of significant interest.

Mr Hallett said people often don't realise the sheer weight involved in storing rainwater which weighs a tonne for every thousand litres.

"It is not unusual to see a 2500 litre water tank on an old timber tank stand in the Dandenongs. This combined with the tank quickly filling with heavy rainfall then weighing two and half tonnes on a timber frame in softened earth and a recipe for a disaster is the result.

"Raised water tanks on timber structures require ongoing safety assessments to check for any deterioration of the timber or any sign of the tank starting to lean."

Mr Hallett said that with heavy rains tanks can fill quickly and within a few minutes double the weight of the water they hold and in turn increase pressure on the structure of the tank itself and also the tank stand or support.

"A falling two tonne tank of water could severely injure or kill a person. It might even endanger the structural integrity of the home if it fell onto the house or crashed into high timber stumps of a house built on a steep slope."