Roof-Harvested Drinking Water Surveillance Using Metagenomics and qPCR in the Ngāi Tahu Takiwā — The Association Specialists
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  2. Oral Presentations - Climate, environment and human health 2
  3. Roof-Harvested Drinking Water Surveillance Using Metagenomics and qPCR in the Ngāi Tahu Takiwā

Roof-Harvested Drinking Water Surveillance Using Metagenomics and qPCR in the Ngāi Tahu Takiwā (23889)

Gabe Mulcare 1 2 , Tim Chambers 1 2 , Shaun Ogilvie 1 2 , Brent Gilpin 3
  1. Ngāi Tahu Research Centre, Christchurch, Canterbury, New Zealand
  2. University of Canterbury, Christchurch, CHCH, New Zealand
  3. New Zealand Institute of Health and Forensic Science , Christchurch, Canterbury, New Zealand

Background

Roof-harvested rainwater is widely used in Aotearoa New Zealand for drinking water but presents potential public health risks due to microbial contamination. Current microbial water quality testing relies on 19th-century technology, primarily monitoring total coliforms and Escherichia coli, which fails to capture the full spectrum of potential pathogens. Genetic approaches such as metagenomics and qPCR are redefining water quality management through comprehensive microbial profiling and targeted detection of microbes. This study applies approaches investigate roof-harvested water supplies to address gaps in microbial risk assessment and support future epidemiological investigations.

Method

A longitudinal audit of domestic self-supplied roof-harvested rainwater systems was conducted in a coastal Ngāi Tahu community. Households were sampled at two time points to assess seasonal variation. Water samples were analysed using standard indicator testing (E. coli, total coliforms), metagenomic sequencing to characterise microbial communities, and qPCR targeting host-associated faecal markers.

Results

Routine testing showed widespread contamination in the initial sampling round, with untreated sites recording 11/15 E. coli and 15/15 total coliform (TC) exceedances, while UV-treated systems showed minimal contamination (0/3 E. coli, 1/3 TC). In the second round, contamination at untreated sites decreased substantially (2/15 E. coli, 9/15 TC), while UV-treated systems remained compliant (0/3 exceedances), indicating temporal variability consistent with seasonal influences. Metagenomic analysis revealed highly diverse, site-specific bacterial communities, including potential pathogens such as Legionella and enteric pathogens. qPCR detected avian markers, indicating bird-associated faecal contamination consistent with community concerns.

Conclusion
Traditional indicator-based monitoring may underestimate microbial risk in roof-harvested rainwater systems. Integrating metagenomics and qPCR has the potential to enhance epidemiological assessment by identifying contamination sources and exposure pathways. The results will inform future epidemiological investigations into the disease burden associated with roof-harvested rainwater systems in Aotearoa. These findings also support the development of enhanced monitoring frameworks for domestic self-supplies in Aotearoa.