So how has council funded the difference? By borrowing, through efficiencies and some risk-taking. But by its own admission, this situation can't be sustained.
This week, the council signed off on its 2013-14 Annual Plan which will see it draw in about $46 million in rates revenue. For the same term, council's debt level sits at $105 million.
But the three years after that, the scenario gets worse, with debt estimated to hit $124 million in 2014-15, $127 million (2015-16) and $131 million (2016-17).
What's created this situation?
The biggest contributors are the wastewater treatment scheme and the stormwater separation aspect of that work. In fact, debts from the stormwater separation stand at $36.6 million with another $20.5 million owed on wastewater treatment.
Also to be added in are $14.5 million for the city water supply, $8.6 millon for roading, $4.2 million for parks and reserves, and $3.7 million for swimming pools.
Rob Vinsen, chairman of the council's strategy and finance committee, says compounding things are problems at the wastewater treatment plant (WWTP) on Airport Rd, which are expected to cost $24 million, and earthquake strengthening of public buildings, another $20 million. Without these multi-million-dollar millstones, the financial forecast would have been much more benign.
"It would have actually been better than forecast in the 10-Year Plan (2009-19)," Mr Vinsen said.
If there's a silver lining, it has to be the sale of Energy Direct to TrustPower, which reaped about $17 million. That allowed council to wipe out the majority of debt in Wanganui Holdings Ltd, its commercial arm.
Retaining the infrastructure side of the business - GasNet - gives council a guaranteed annual dividend that could prove to be a cash cow.
Council is also looking at other saleable assets, including 32 properties which have an estimated market value of $6.6 million. They are what Mr Vinsen called "low hanging fruit" and could be sold quickly.
He said another positive was likely to emerge with Wanganui's port.
Council paid $2.5 million to buy out the lease of the port and, while there was no immediate prospect of recovering that money, he said the future could bring an option to sell assets in the port in a partnership arrangement.
"We haven't got much we can grasp at in that regard but I think there's a prospect in the offshore mining that's being investigated. The potential for Wanganui as a service centre for that is substantial."
Meanwhile, council has ramped up the trade waste levy for those wet industries that discharge into the WWTP to $2.25 million this year. That's an increase of 40 per cent on last year's $1.6 million.
"This may force changes among those industries and they may decide it's more economic for them to do more pre-treating. But they're so important to our economy that we just have to work together.
"We couldn't face a closure of an Imlay or a Tasman Tanning. The numbers they employ and what it means for our economy are too big."
Mr Vinsen said council also needed to carry out an activity and service review across every council operation, identify the savings and implement those in the 2014-15 plan.
He said rating and debt levels were inextricably related: if rate levels were too low, then without a corresponding drop in service levels there was insufficient funding available to maintain a debt repayment programme.
"Differing rating levels between the three sectors - residential, farming and commercial - reflect the activity where debt is incurred. Farming does not contribute to the wastewater scheme but can be affected by storms which impact on rural roading.
"And commercial is heavily influenced by council's economic development activity. In the case of the $2.5 million i-Site, 75 per cent of the cost was from that small number of commercial ratepayers."
But the major cause of Wanganui's increasing debt level was the cost of cleaning up the Whanganui River. Spending on the treatment and separation cost the ratepayers about $120 million, with this expenditure spread over 30 years.
Before 2004, the council rated in advance for the scheme, building up a fund in the bank of $4 million which reduced the need for borrowing at that time. But the really big costs didn't start to occur until about 2005.
"It would not have been possible to fund the scheme on a pay-as-you-go basis at that time as rates would have been astronomical," he said.
Mr Vinsen said despite those debt levels he was "not a panic merchant".
Council had imposed policy limits which meant net debt would be no more than 200 per cent of income and this year's debt - at 151 per cent - was well under that.
"Another limit is that net interest should not be more than 15 per cent of income and the 2013/14 Annual Plan is also well under that limit (9.4 per cent)."
He remains an advocate of "inter-generational equity" in terms of borrowing for such large projects, arguing it's unfair for today's ratepayers to fund assets that future generations would also enjoy.
So what is the district council doing about that debt?
Apart from sale of Energy Direct NZ, retaining GasNet - the gas infrastructure - will provide a dividend of around $1.5 million to $2.5 million annually; unbudgeted income that wasn't allowed for in previous Long Term Plans.
Council has cut another $1.083 million from the Annual Plan, including $275,000 in staff costs, and $100,000 in community grants. It has also deferred $4 million in borrowing for the earthquake strengthening programme.
But all these aren't enough.
Blindsided by the WWTP upgrade and the quake strengthening demands means the district faces frightening rates hikes in 2014-15 and again the year after, in the order of 7.9 per cent and 8 per cent respectively.
The bulk of quake-proof funding spent this year - about $2 million - is involved in relocating the Sarjeant Gallery to temporary premises. Mr Vinsen said council could still remove the future $18 million for seismic strengthening from its long-term plans and this would bring about a major - but temporary - reduction in future rates. But he believed government will compel local authorities to start upgrading sooner and not later.