"A significant portion of this new debt would be sourced from the LGFA which offers interest savings for those councils with favourable credit ratings," he said.
"And given we'll need funding for the $24 million wastewater treatment plant upgrade, this rating will be helpful."
It is the first time the Wanganui council has had a credit rating. "At a time when it's hard to get some investors to invest, a credit rating does make a difference."
But Mr Harkness warned that a downward trend in the rate "would not be good".
Getting access to a bigger pool of lenders is the prime reason behind the decision to secure an internationally-recognised credit rating.
It is a move that will cost about $50,000, with ongoing annual costs of a similar amount, but council officers say that will be more than compensated through interest savings that would follow from achieving a credit rating.
At the moment about 60 per cent of the country's councils have credit ratings, ranging from AA to A+.
Mayor Annette Main called the credit rating was a vote of confidence in council's "prudent financial management, budget flexibility and transparency".
Ms Main said it would also give added confidence to the council's bond holders.