Water scarcity, a critical threat to sustainable development, is particularly pronounced in China, where per capita water resources are a quarter of the global average. Previous assessments often focused on water quantity, neglecting the crucial role of water quality in usability. China's rapid economic growth has caused widespread pollution from land use changes, untreated wastewater, and agricultural runoff. While some studies acknowledged water quality's influence, they lacked quantitative analysis. This study addresses this gap by comprehensively assessing water scarcity in China, considering both quantity and quality at various temporal and spatial scales, incorporating environmental flow restrictions. This multi-scale approach is vital for effective policy-making and regional water management strategies.

Existing literature on China's water scarcity mainly focused on quantitative assessments at regional and national levels, overlooking the significant constraints imposed by water quality degradation. While some studies mentioned water quality as an influencing factor, they lacked comprehensive quantification of its impact on water scarcity. This study builds upon previous research by explicitly incorporating water quality requirements into the assessment framework, providing a more realistic and comprehensive understanding of water scarcity in China.

This study quantified China's water scarcity by integrating water availability, water quality (COD, NH4-N, EC), and sectoral water withdrawal data (irrigation, industry, domestic, and eco-environmental compensation) at multiple scales (0.25° × 0.25° grid cells, first- to third-order basins) and time scales (annual, seasonal, monthly) for 2012–2016. Water scarcity was assessed using three metrics: quantity-based water scarcity (WSqua), pollution-induced water scarcity (WSpol), and combined water scarcity (WScom). WSqua is the ratio of water withdrawal to available water after accounting for environmental flow requirements (EFR). WSpol quantifies the additional water needed for dilution to meet water quality standards. WScom combines WSqua and WSpol. Data were compiled from various sources, including the national environmental monitoring network, hydrological model simulations, and statistical yearbooks. Spatial interpolation techniques and downscaling methods were employed to create consistent datasets across different scales. The Theil index was used to measure regional inequality in water scarcity.

The study's key findings reveal that incorporating water quality significantly exacerbates water scarcity in China. At the grid cell level, WScom increased the area and intensity of water scarcity compared to WSqua. North China experienced consistent water scarcity due to both insufficient quantity and poor quality. South China, while having sufficient water quantity, suffered seasonal scarcity due to quality issues. Basin-level assessments corroborated these findings. The Huai, Hai, Yellow, and Liao River basins showed high proportions of areas under WSpol and WScom. The impact of water quality was particularly striking in the Hai River basin, where the inclusion of water quality more than doubled the WScom value. Seasonal analysis showed that spring was the most water-scarce season. Sectoral analysis revealed that agriculture was the most water-intensive sector and most vulnerable to scarcity. Population-based analysis revealed that a substantial portion of China's population (between 31.1% and 86.1% annually, and significantly higher seasonally and monthly) faced water scarcity conditions. Regional inequality analysis showed that water scarcity was much more severe in North China compared to South China, with the Theil index indicating greater inequality when water quality was considered. The study demonstrated that incorporating both water quantity and quality provides a more comprehensive and realistic assessment of water scarcity in China, highlighting the importance of managing both aspects for sustainable water resource management.

The findings highlight the critical need to integrate water quality considerations into water scarcity assessments. The significant impact of pollution on exacerbating water scarcity and inequality underscores the importance of targeted pollution control measures. The results provide crucial evidence for policy-making, indicating the necessity of comprehensive water resource management strategies that address both quantity and quality issues. The multi-scale approach provides valuable insights for regional planning and water allocation strategies, guiding targeted interventions where water scarcity is most severe. The analysis of sectoral water scarcity highlights the vulnerability of agriculture and the potential for water conservation in this sector. The large proportion of the population affected underscores the urgency of addressing water scarcity for ensuring social and economic development in China.

This study demonstrates that incorporating water quality significantly aggravates China's water scarcity problem and its regional inequality. The findings highlight the need for integrated water resource management strategies targeting both water quantity and quality. Future research could focus on more detailed modeling of specific pollution sources and their impacts, exploring advanced water treatment technologies, and developing effective policies for sustainable agricultural water use.

The study's spatial resolution (0.25° × 0.25°) limits the ability to capture highly localized water scarcity events. The data used were collected from monitoring networks, which may not fully represent the spatial variability of water quality across the entire country. The dilution approach for assessing quality-induced water scarcity may have certain limitations in fully capturing the complexity of water quality impacts on different water uses.