Potential Health and Environmental Risks Associated with Onsite Greywater Reuse: A Review

The practice of decentralized, on-site greywater (GW) treatment, the non-toilet portion of domestic wastewater (WW) stream, has become widespread with millions of systems in use worldwide. GW reuse can bring a significant reduction in domestic and urban water demands and increase the exploitation efficiency of this scarce resource. However, environmental and human health concerns challenge onsite treatment, as its operation by non-professionals must be reliable, simple and economically feasible if such systems are to be used by many. While macro- and micro-pollutants found in GW are the main hazard to environmental health, pathogens are considered the principal risk to public health. Hence, a few major topics related to GW reuse are discussed in this review: (a) microbial and physico-chemical quality of GW before and after treatment; (b) plant health after GW-irrigation; (c) soil health risks as measured by changes of quality following GW irrigation; and (d) risks to public health via epidemiological data and quantitative microbial risk assessment (QMRA).