A claim that Canterbury has 70 per cent of New Zealand's freshwater has been dismissed by a Christchurch hydrologist.

A review of Environment Canterbury's (ECan) performance, led by former National deputy prime minister Wyatt Creech, said that "around 70 per cent of New Zealand's freshwater resource is in the Canterbury region, much of which is under demand from competing interests".

Daniel Collins, who writes the Crikey Creek blog and is a hydrologist for the Crown research institute National Institute of Water & Atmospheric Research, said the figure was wrong.

He said the best measure of freshwater resource was precipitation, including snow.

"I bet we don't have more than the West Coast," Collins said.

"You've got to give people the benefit of the doubt – there's been a mistake somewhere."

ECan surface water scientist Adam Martin agreed the Creech report claim did not seem correct.

"Based on the information from the Statistics New Zealand website and the calculation on the blog, the value is between 10 per cent and 15 per cent, depending on which inputs and outputs are selected."

Last week, Creech said the figure referred to the "allocable resource" in New Zealand – freshwater which can be gained by applying for a resource consent – and it came from the Ministry for the Environment.

However, regional and Government figures showed the region allocated between 55 per cent and 58 per cent of New Zealand's freshwater.

Collins said the "resource" had been confused with Canterbury's irrigated land.

A ministry spokeswoman confirmed the 70 per cent referred to "Canterbury's approximate share of the total land irrigated with freshwater in New Zealand".

She referred to two reports: the Canterbury water management strategy stated "70 per cent of New Zealand's irrigated land is in Canterbury"; and the ministry's 2006 Snapshot of Water Allocation in New Zealand, which said Canterbury had 66 per cent of the New Zealand's total consented irrigated area.

Collins said it was ironic that the Creech report, which assessed ECan's ability to manage freshwater resources, got the freshwater figure so wrong.

"And, unfortunately, people probably now think it's true," Collins said.

- © Fairfax NZ News