Green MP and Minister Eugenie Sage has been accused of "selling out" by her own party over a decision to allow a Chinese-owned company to expand its Bay of Plenty water-bottling plant.

Sage has been forced to defend the decision she made as Land Information Minister, along with Associate Finance Minister David Clark, to allow Cresswell NZ Ltd to buy land to expand its Otakiri Springs water-bottling plant near Whakatane.

Cresswell NZ is owned by Chinese water bottler Nongfu Spring.

Following a backlash from Greens supporters and former Green MPs on social media, Sage told reporters today that she had to make difficult decisions as a minister and her personal feelings about the issue were irrelevant.

"I'm aware there's a lot of concern on my Facebook page and elsewhere on social media. 
"It was a hard decision that I thought long and hard about."

Co-leader Marama Davidson said Sage had been constrained by the Overseas Investment Act in making the decision.

"The minister was constrained by a flawed Act which says we are unable to take environmental and Treaty decisions into account. This decision does not sit with Green kaupapa and longstanding Green Party position," Davidson said.

"We don't like it and even the minister has been upfront about the constraints. We will continue to lobby for water bottle levies and for ensuring we have better understanding of environmental, Treaty and economic gains working together in these decisions.

She said it was obvious party members were unhappy with Sage's decision and some were 
angry. "This is understandable."

Co-leader James Shaw said he understood how people felt.

"People have been really concerned about water allocation issues and in particular around the water-bottling situation."

The Government was working on it but had yet to get to dealing with the issue, he said.

Former Green MP Sue Bradford tweeted a warning to the party; "Do the parliamentary Greens have any idea of the danger they're in? Even in govt there is almost always room to compromise - & even fight – vs such unpalatable decisions. Betrayal on water bottling a sad day for Green voters."

Another Twitter user said: "Please Stop Eugenie Sage Shes Selling us out". (sic).

Sage herself explained her decision in a blog post on the Greens' website yesterday.

"Some people might wonder why a Green MP who is a minister has allowed such a land purchase involving a water bottling plant to go ahead," she wrote.

"Basically the law is clear about what ministers can and cannot take into account. We had to consider "substantial and identifiable" benefits to New Zealand. That's jobs, exports, greater productivity and additional capital investment for the country."

The decision, which is conditional on the company providing an additional 60 full-time jobs and getting the resource consents it needs, means Creswell NZ can buy 6.2ha of sensitive land at Otakiri.

Clark said the Overseas Investment Office recommended approval as Creswell NZ Ltd met the test to provide substantial and identifiable benefits to New Zealand.

The company proposes to expand the existing water bottling plant and invest more than $42.5 million over four years to upgrade the plant and establish two new bottling lines. The expansion is expected to provide 32 jobs within two years and 60 full-time jobs once the new plant is fully operational within four years.

"This is a substantial increase on the current eight jobs at the plant and offers employment opportunities for the Whakatane community and Bay of Plenty region," Clark said.

Save our Water Otakiri last year estimated the new production line would fill 154,000 bottles an hour, 24 hours per day, 365 days of the year."

That equated to more than 3.5 million bottles per day, or 1.35 billion bottles a year, the group said.