*Review* **Diversifying Water Sources with Atmospheric Water Harvesting to Enhance Water Supply Resilience**

**Mengbo Zhang, Ranbin Liu \* and Yaxuan Li**

Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Key Laboratory of Urban Stormwater System and Water Environment (Ministry of Education), Beijing University of Civil Engineering & Architecture, Beijing 100044, China; zmb11211324@163.com (M.Z.); fank812@hotmail.com (Y.L.) **\*** Correspondence: ranbin\_liu@hotmail.com

**Abstract:** The unequivocal global warming has an explicit impact on the natural water cycle and resultantly leads to an increasing occurrence of extreme weather events which in turn bring challenges and unavoidable destruction to the urban water supply system. As such, diversifying water sources is a key solution to building the resilience of the water supply system. An atmospheric water harvesting can capture water out of the air and provide a point-of-use water source directly. Currently, a series of atmospheric water harvesting have been proposed and developed to provide water sources under various moisture content ranging from 30–80% with a maximum water collection rate of 200,000 L/day. In comparison to conventional water source alternatives, atmospheric water harvesting avoids the construction of storage and distribution grey infrastructure. However, the high price and low water generation rate make this technology unfavorable as a viable alternative to general potable water sources whereas it has advantages compared with bottled water in both cost and environmental impacts. Moreover, atmospheric water harvesting can also provide a particular solution in the agricultural sector in countries with poor irrigation infrastructure but moderate humidity. Overall, atmospheric water harvesting could provide communities and/or cities with an indiscriminate solution to enhance water supply resilience. Further research and efforts are needed to increase the water generation rate and reduce the cost, particularly via leveraging solar energy.

**Keywords:** water supply resilience; atmospheric water harvesting; fog collection; refrigerated atmospheric water extraction; climate change
