Integrated systems for rainwater harvesting and greywater reuse: a systematic review of urban water management strategies

Combined, decentralized systems for rainwater harvesting and greywater reuse may enhance the water security of urban areas by reducing dependence on the main water supply, in particular during critical periods, such as the dry season. They can also minimize the risk of flooding during the rainy season. The present study assesses the accumulated knowledge of these combined systems based on a systematic review of the literature restricted to academic sources. The review revealed knowledge gaps that must be resolved to better assess the optimum combination of rainwater and greywater recovery, how this affects the need for the treatment of the recovered water, its final quality, potential options for reuse, water economy, and the environmental and economic performance of the system. Further empirical studies are required to determine the most adequate design configuration for these systems, considering their multiple objectives, technological perspectives, and in particular, their potential for improving environmental shortcomings. There is a clear need for widespread use of low-impact technologies to ensure the most effective possible results. Water recovery systems will become increasingly important as a means of tackling the challenges of water supplies in the urban landscape, which are being exacerbated by climate change.