The Energy-Quality Nexus in Atmospheric Water Generation: A Review of Contaminants, Performance Metrics, and the Proposal of the AWEQI.

Atmospheric water (AW) is currently recognized as a promising solution to mitigate the global water crisis. Nevertheless, its harvesting techniques should balance three main aspects: energy consumption, yield, and the quality of produced water. Water quality is of the utmost importance, because the potential uses of atmospheric water-and therefore its value-ultimately depend on this characteristic. Currently, existing indices and indicators intended as evaluation tools for different harvesting techniques generally focus on the first two aspects only, overlooking the quality perspective, with the risk of overestimating the performance of systems that require less energy but provide low-quality water. This study fills this knowledge gap by proposing a new evaluation tool, the Atmospheric Water Energy-Quality Index (AWEQI). This index links the energy evaluation of an Atmospheric Water Generator (AWG)-a term referring to all active, passive, or hybrid systems for atmospheric water collection-to the quality of the produced water. The index is constructed through an appropriate reformulation and combination of the Water Energy Transformation (WET) indicator and the Water Quality Index (WQI) to obtain a monotonic function whose values increase with improved performance, both in terms of energy efficiency and water quality. Moreover, based on a literature review, the study presents an analysis of potential AW contaminants and their sources, and proposes two parameter sets to be considered in the WQI calculation.