Damage to the electronic control units was the major reason a car was deemed too damaged to repair, AIG spokeswoman Shelley Huang said.
''Dependent on the volume of water and level of contamination, this is very much a clear-cut protocol to write [the] vehicle off,'' she said.
''... it only takes a small volume of water to render these components faulty.
''We take customer safety and frustration etc into consideration when making a decision on total loss.''
AMI Insurance Octagon branch manager David Shead said several hundred claims for flood damage had been filed at the insurer's three Dunedin branches.
Most cars assessed were no longer roadworthy.
''If there was water inside the car, then they are being written off.''
Most were because of electrical faults in the cars, he said.
Cars damaged by water were unsafe to drive because the electrics were probably affected, he said.
Braam Kruger, the Dunedin branch manager of global loss adjusting and claim management company Cunningham Lindsey, said it had ''dealt with a number of flood-damaged vehicles and most of them had to be written off''.
