A water lobby group doubts a tax on water would affect trade negotiations.

Labour made big promises before the election to tax exports of bottled water.

However, a leading trade negotiator has told MPs if they follow through with their promise, it would break trade agreements, including that with China and the revised TPP.

Water New Zealand CEO John Pfahlert told Rachel Smalley it seems unlikely this would be the most pressing issue for the Government, because there's a bit of give and take in trade deals.

"It's hard to imagine that taxing bottled water was the most important issue to put on the table as a sort of leverage for other countries to make movement on other things that are of importance to us."

LISTEN TO JOHN PFAHLERT TALK WITH RACHEL SMALLEY ABOVE