Nature-based Solutions for greywater reuse in water-scarce urban areas: A case study from Iran

Globally, 2.2 billion people lack access to clean drinking water, and about half of the world’s population experiences seasonal water scarcity. Iran, one of the world's driest countries, faces significant water management challenges. This study examined the potential of Nature-based Solutions (NbS), such as constructed wetlands, for sustainable greywater treatment and reuse in Mashhad, Iran. Through a comprehensive survey of 137 participants, the study assessed awareness, willingness, and barriers to NbS implementation. The findings revealed a moderate public awareness of NbS and greywater reuse (e.g., 59% familiar with greywater reuse, but only 34% aware of constructed wetlands). However, this limited knowledge was contrasted by strong support (86%) for NbS implementation and a high willingness (73%) to adopt treated greywater for non-potable purposes. Key barriers identified include high costs, lack of expertise, and public resistance due to health concerns. Financial incentives, such as government subsidies and low-interest loans, were recommended to overcome cost-related obstacles. The use of cost-effective materials and innovative technologies, such as hybrid wetland systems, could further improve the feasibility of NbS. This study's novel finding is the high social potential for NbS in a water-scarce, semi-arid context, where significant public support outweighs knowledge deficits. These results establish Mashhad as an example for designing socio-technical adoption frameworks applicable to urban centers facing intensifying water challenges across the MENA region.