Summary

Water scarcity is an emerging issue in New Zealand. Wastewater can be treated and reused to reduce the use of potable water and freshwater resources, providing an alternative source of water for agriculture, urban activities and use by industry. However, while wastewater reuse provides benefits as an alternative source of water and nutrients, it also presents potential risks to human health and the environment. Guidelines have been developed internationally to manage the risks associated with wastewater reuse. The World Health Organization (WHO), the Food Agriculture Organization of the United Nations (FAO), the International Organization for Standardization (ISO) and the European Union (EU) have developed international guidelines. Whilst New Zealand has national guidelines for the application of sewage effluents, sludges and biosolids to land and regional guidance for the reuse of wastewater from small, onsite wastewater systems, there are no appropriate guidelines for reuse from municipal wastewater treatment facilities, or for reuse of wastewater in agricultural, urban or industry applications. In the absence of New Zealand guidelines for wastewater reuse, there is the potential for inconsistent and/or inappropriate regulatory decisions. This review compares international guidelines for wastewater reuse with a focus on the risk to human health and the use of a risk assessment approach. It compares the different criteria for wastewater treatment in the international guidelines and standards and how the criteria and other preventive control measures, or barriers, are combined to reduce risk. It also discusses the differences in risk attributed to different combinations of wastewater treatment and preventive controls. Monitoring requirements to ensure risks are managed are also compared. The focus is microbial risk, as it is a greater risk to human health risks from reuse of wastewater, compared to chemicals. Reuses for urban, agricultural and industrial reuse are covered, but it is important to highlight that Māori have established cultural traditions and associated customary practices for managing human waste, particularly to relation to keeping it separate from food. Not all wastewater reuses may be acceptable.