The regulation of soil water retention by biochar amendment has been concerned especially in cropland ecosystem. However, the quantification of biochar's effects on soil hydrological properties and crop water use efficiency (WUE) is still limited, and the factors driving the biochar effect need to be investigated. Based on a database with 681 observations, meta‐analysis and structural equation model (SEM) were employed to reveal how biochar amendment affects water supply capacity and WUE. The results showed that biochar application increased available water content (AWC) and WUE by 26.8% and 4.7% on average, respectively. According to the SEM of AWC (R2 = 0.70–0.96), the increase of soil organic carbon (+36.1%) by biochar application can not only directly improve AWC but also indirectly improve AWC by affecting permanent wilting point (−1.0%) and mean weight diameter (+11.1%). The SEM of WUE (R2 = 0.74) indicated that soil moisture and porosity were increased by 10.8% and 7.0% under biochar amendment, which was the reason why biochar improved WUE. This study emphasized that biochar can improve soil hydrology and crop yield by increasing soil water supply conditions. And a rational rate of biochar is the precondition to obtaining the benefits of soil hydrology, otherwise, the excessive use of biochar may lead to the decline of WUE.

Water scarcity threatens the health and development of countries worldwide due to the rapid expansion of population and climate change, pushing the government to find more innovative and sustainable ways to address water stress. Governments have adopted reverse Osmosis (RO) seawater desalination technology for its cheap raw water intake and stability. However, its environmental and financial sustainability remains disputable. In this study, three metrics, carbon footprint, cost, and waste discharge, are defined and analyzed to identify which water supply technology has greater prospects. Accounting for a full water treatment process from raw water intake to transportation and distribution, the RO desalination plant outruns traditional water treatment facilities due to less carbon emission, limited operation cost and maintenance, and less hazardous waste discharge. The qualitative and quantitative analysis of environmental and financial sustainability of existing solutions to the water supply may provide a more comprehensive understanding and further supports policy making.