In the 2017-18 year, the Auckland Council plan reveals that its cost of finance - interest in other words - will be equivalent to more than 30 per cent of its rates revenue.
The Auckland Council Plan - like the Kaipara District Council Plan - assumes a very high rate of growth. It assumes that developer levy revenues for example will increase by a factor of four over the next five years, to$221 million in 2017. It also assumes that Watercare's revenues will increase by over 35 per cent in the same period. But what happens if that high rate of development and growth does not eventuate?
The global financial crisis has not gone away. But what happened in Mangawhai is a canary in the local government coalmine. A prudent council should not be betting on growth today.
Sewage management and wastewater treatment is a core responsibility of local government. Many small communities are under pressure to switch from local onsite systems to council controlled community schemes.
Large centralised sewage systems are expensive to build and - as environmental expectations increase - alarmingly expensive to maintain. North Shore City Council discovered this when community pressure obliged it to fix its network and prevent wet weather overflows from sewer pipes which were closing local beaches.
The council investigated sewer augmentation options not unlike Watercare's proposed Central Interceptor Tunnel, but rejected them on the basis of cost.
Instead it adopted a dual programme to reduce stormwater infiltration into its sewer network, and to build underground storage tanks which collected the most damaging and frequent overflows. When the storm has passed and the sewer network has drained sufficiently, the collected wastewater can be pumped to the treatment plant.
The benefits of this approach were many. It was not capital intensive and could be funded from rates revenue. It was an approach that could be staged - environmental benefits were immediate when the first overflow storage tank was constructed. It allowed for a de-centralised approach to network management - which lent itself to computer control in response to concentrated weather events.
Watercare would do well to study North Shore's experience.
My assessment suggests savings of over $500 million for the whole project, but it may be that through staging the project over time, the benefits might be even greater.
Joel Cayford is an urban planner and a former city and regional councillor.