"Because I'm not insane," she said when asked why.
The $600 million for the new water policy would come from the party's recently announced National Infrastructure Bank – its mooted state-run bank for central and local Government infrastructure projects.
National's plans involve targeting the 98 per cent of flowing freshwater in New Zealand that is currently not captured.
To do this, the party would provide loans or take a stake in water storage projects – that money would be paid back over time so the money could be recycled and spent on more projects over time.
"Done correctly, water storage can be equal parts beneficial to the environment, economy and community," National leader Judith Collins said.
The party is also doubling down on its long-held belief that "water is owned by no one" – Labour's position is that everyone owns it.
National would work with iwi to make sure they had access to water, Collins said, but "it is a stake in the ground here; that water belongs to all New Zealanders."
That position was quickly condemned as "pure cowardice" and "dogwhistle politics" by Geoff Simmons, leader of the Opportunities Party (TOP).
"They are obviously too scared to have the crucial discussions with tangata whenua over water rights, and are obviously happy to continue to allow Chinese water bottlers like Cloud Ocean Water in Christchurch to take water for free and sell it to the tune of $4.3 billion per year," Simmons said.
"They say they will 'guarantee common ownership of water' which is code for saying that the National Party is not willing to have the hard discussion around the ownership and management of our valuable fresh water...they will never consider Te Tiriti o Waitangi a binding document. This is a new low, even for National."
Collins used the recent Auckland water crisis as an example as to why this planned spend was important.
"Cities like Auckland need a resilient and clean water supply to continue being a world-class city, and to make sure we can deal with the economic crisis we are facing.
"We get a lot of rainfall in New Zealand...we don't have the storage. Our problem in New Zealand is primarily around storage....it takes money to do these things.
"National wants a strategy and model that allows us to unlock our economic potential and safeguard our communities from increasing drought."
National's environment spokesman Scott Simpson said that at the moment, less than 2 per cent of the water that flows over New Zealand is captured.
Of that, half is used in towns and cities while the rest is used for irrigation.
"Our country has water, we're just not using it," Simpson said.
"We can't keep letting our water flow out to sea while our towns run out of water and our farms dry up."
The water policy uses Kerikeri as an example of a scheme which has worked well – one it wants to see replicated across the country.
"It is estimated that the Kerikeri water storage scheme alone provides 2.5 per cent of the GDP of the Far North," the policy says.
"It is not a coincidence that Kerikeri South has the lowest levels of deprivation in the Far North and the best access to water."
National has also promised to develop a National Policy Statement on Water Storage.
Collins said this would provide certainty around the strategic use of water, streamline consenting and set minimum environmental standards for newly irrigated land.
On wider questions about balancing spending promises, Collins was asked if National viewed the money set aside by the Government for the future Covid-19 response as fair to spend in other areas.
Collins said there wouldn't be more widespread outbreaks under her Government.
"In the fiscal plan, everything is accounted for and we are very clear about that.
"The Covid fund is simply borrowed money. Whether you stick a label on it...it still has to get paid back."
