Adding Clarity To The Murky World Of Greywater Re-Use And Risk To Human Health

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/day) of residential water demand is water that is available for re-use. If re-used 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 both property owners and water service providers. Using alternative water sources has the potential to reduce network demand and increase resilience, 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 re-use 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 re-use 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.

A further barrier to uptake is lack of legislation, with inconsistent guidance for home and business owners regarding re-use of greywater throughout New Zealand. A 2011 survey of regional councils found that the majority permit the discharge of greywater to land without a resource consent. However, it was found that some of these regional councils deal only with discharge to land, and not re-use of greywater. In these instances, re-use was reported to be a function of the district council. On the contrary, many of the district councils that responded considered greywater re-use to be a function of the regional council. Thus, highlighting the inconsistencies. There are no national guidelines for greywater re-use at present.

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

It is the overall aim that this research will provide more context around greywater re-use and any potential impacts to human