SR420 Microbial water quality of commercial and residential greywater sources (April 2019)

A large proportion of residential and commercial water use could potentially be substituted with alternative water sources, such as greywater. In the Kapiti Coast area, it has been reported that 68% (160 litres per person per day) of residential water demand is water that is available for reuse. If reused, this represents a large proportion of a household’s daily water use that does not need to be sourced from the reticulated network. Greywater reuse provides benefits for property owners and water service providers. Using alternative water sources has the potential to reduce network demand, increase resilience and reduce wastewater peak flows and could allow outdoor water use to continue in periods of drought.

Given the increase in water shortage experienced across New Zealand, alternative solutions to the reticulated network should be assessed for their suitability for reuse. However, there are several barriers to uptake of greywater reuse that require more research. Predominantly, people’s perception of risk from waterborne disease, water quality and human health risk were identified in a 2014 industry survey as the biggest barrier to greywater reuse in New Zealand. A subsequent water quality and human health risk analysis found better than expected water quality results, although it was highlighted that more work was required to make this representative.

This study seeks to expand on previous research by assessing microbial water quality from a range of greywater sources, including greywater from residential and commercial properties. Taken weekly over 6 months, greywater samples were tested for Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) and compared to international greywater reuse guidelines.