"A lot of work" needs to be done before the country can get to a point where it charges for water, says Prime Minister Bill English.

The Government has asked a group of experts to look into whether to introduce a charge for water exports, following a public outcry.

Prime Minister Bill English says "growing public concern" is behind the decision, after protests around the country and a petition calling for a moratorium on bottled water exports.

At his weekly media conference, English said the Government was writing to the Ministry for the Environment's water allocation technical advisory group, asking it to consider "the issues around exporting water".

Lawrence Smith Environment Minister Nick Smith has no interest in charging companies for water.

"We do accept there's growing public concern about it, that's why we want to refer it off to this group to look at what if any reasonable options there are.

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"We just don't want to give the public the impression that there's a simple easy answer, because we'll almost certainly find there isn't - if there is, then we'll see where that goes."

The group had already been looking at how water use was allocated, but its focus had been primarily on water quality and large users like farmers, he said.

"We're not setting up a group now to deal with this issue - it's been in place and it follows on from all the published work of the Land and Water Forum, follows on from all the work around the water quality framework and all the legislation that's related to that, so we're just asking them specifically to look at this."

The Government's experience had shown water issues were "always five times more complicated than you thought", and English did not underestimate the challenges involved in dealing with exports.

"On the one hand, there is real public concern about foreign companies' access to water, on the other hand there's' a long-held, deep-seated view among New Zealanders that no-one owns it and it's free, so we'd want to step through any process carefully."

Maori water interests and rights would need to be part of the discussion, along with whether a charge could be levied without establishing who legally owned the water.

"As we've discussed, New Zealand's long-held position has been, no-one owns the water and no-one pays for water - they pay for consents, they pay for infrastructure, but water in itself is free, just as it is for our electricity users and businesses who use it."

English said it currently did not matter whether or not it was fair to profit off water, as long as consents were "consistent with New Zealand's legal framework".

He would not say when the Government would take any action on the issue, with the advisory group to report on a range of water issues in late 2017.