A Proposed Framework for Forecasting The Demand for Urban Water In New Zealand

The 2010 Auditor General’s investigation into how we plan to meet the forecast demand for drinking water identified that Councils apply a range of approaches. Of eight Councils studied, only three were identified as effectively managing their drinking water supplies. The variation in approaches taken to demand forecasting was also an issue identified by the 2012 PwC/GHD study carried out on behalf of WaterNZ. 

The 67 Local Authorities across New Zealand that operate urban water supplies face a range of challenges. Some have rapidly growing populations and others populations that are diminishing. In some locations irrigation and industrial demands are large compared to urban needs. Many face challenges of aging infrastructure or peak demand pressures.

The use of a common approach across New Zealand to forecasting the future demand for water would serve Councils well. It would provide a consistent framework to develop a forecast and should clearly identify the potential advantages and disadvantages of decisions. Councils and ratepayers could then have more confidence that investment is appropriate and made at the right time.

This paper explores demand forecast approaches that are relevant to New Zealand. It draws on established frameworks from overseas and the authors’ experience of current practice here.