Private Water Supplies - Where are they and what are the risks?

Ed Burry, Greg Offer – Beca Ltd, Michele McDonald – Christchurch City Council

Christchurch City Council (Council) has been working to identify, assess and prioritise the needs and risks of communities served by private water supplies. A two-pronged approach was adopted, using GIS mapping and onsite investigations to address the many unknowns and knowledge gaps in this area. 

This paper presents the results of Council investigations which brought together GIS mapping outcomes with “ground truthing” at specific sites to build a picture of the drinking water needs of communities not serviced by Council, to define risks related to this and to set the baseline for further work. 

While water supply in urban reticulation networks is relatively simple, the situation can be more complex in rural areas such as Banks Peninsula. Banks Peninsula lies southeast of Christchurch and comprises more than a dozen bays with small towns and settlements. Drinking water networks in these bays are mostly not connected, meaning that each community receives a different level of service. Diamond Harbour, for example, receives drinking water from the Council’s reticulated network, while Purau, a nearby settlement, does not.

A GIS mapping tool was used to identify possible private water suppliers within the Christchurch District. In the modern era a plethora of data is available. The GIS mapping made use of datasets from multiple sources and included the generation of spatial data layers to mechanise the identification of private water suppliers. As a further step, a risk assessment algorithm was developed to produce risk heat maps that greatly assisted understanding the comparative water supply risks faced by discrete clusters of properties. The risk assessment was used to prioritise individual communities for further assessment. The mapping tool is dynamic and allows Council to identify possible private water suppliers and systems on an ongoing basis, as and when datasets are updated. The tool also allows Council to manually identify and record private water supplies and systems, to maintain institutional knowledge and to supplement the algorithm’s findings. 

A needs assessment case study was completed for one of the higher risk un-serviced communities identified - Koukourārata Marae and local Port Levy community - and generated a comprehensive list of water supply service options. These were compared using multi-criteria analysis to determine the suitability of the various options. The outcome assisted Council in its initial planning for servicing the community.

Readiness assessments were undertaken for existing private water suppliers that were willing to participate. This provided useful baseline information on the compliance status of private water supplies in Christchurch. 

Overall, the work has proven a useful starting point, has identified key data gaps and themes, and has provided direction for working towards compliance with the Local Government Act requirement (as amended by the Water Services Act) to perform a needs assessment.