In recent years, biochar has attracted considerable attention owing to its application in disposing a large range of organic and inorganic contaminants from industrial wastewater. In this context, one of the dual benefits from biochar application is greywater footprint reduction in industrial wastewater. The greywater footprint (GWF) is an important indicator tool for the determination of environmental impacts and risks in water pollution and scarcity to reduce climate change effects. The GWF is described as the quantity of fresh water required to dilute the contaminants to meet water quality standards. From this point of view, this study investigated GWF reduction by malt dust-derived biochar in terms of brewery wastewater treatment. The GWF was determined in terms of organic materials removal by considering the parameters of chemical oxygen demand (COD) and total suspended solid (TSS). A data-driven analysis was performed by using Monte Carlo simulation based on the achieved data of COD and TSS removal from brewery wastewater by the agro-industrial biochar adsorption process. At the end of the analysis, a new data-driven parametric index (GWFI_BP) was developed based on the basic GWF tool. A data-driven model based on the parameters of COD and TSS was designed and operated to determine the effect of the dual benefits of the biochar adsorption process compared to the conventional activated sludge process. This tool was used by considering the treatment efficiencies, allowable discharge limits, and legal water pollution procedure. The analysis showed that an average GWF reduction of 21.59% was ensured by using agro-industrial biochar. The highest GWF reduction was observed in terms of COD removal with a value of 30.19%. Also, the malt dust which was the feedstock of the biochar was the by-product of the brewery industry, so a waste reduction was dually achieved with GWF reduction in this study.