Abstract
A first-time comparative scientific literature analysis of monitoring and assessing the surface water quality in five Central Asian (CA) countries (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) was carried out. The methodological approaches, surface water quality parameter, pollution indices and state acts in CA countries were compared, and benchmarked against international frameworks and practices (e.g., those of the EU, USA, and Canada). The methodological framework of the study based on a comparative analytical review of regulatory and methodological documents, official reports of national hydrometeorological services, and international guidelines. The comparison was conducted using standardized criteria (assessment logic, classification systems, quality indices, parameter coverage, monitoring organization, Quality Assurance/Quality Control (QA/QC) procedures, and transboundary comparability). The analysis reveals the emergence of three distinct developmental trajectories of water quality assessment methodologies in the region: a modernization pathway (Kazakhstan), a transitional/hybrid pathway (Uzbekistan), and an approach preserving the post-Soviet methodological architecture (Kyrgyzstan, Tajikistan, and Turkmenistan). A phased harmonization plan is proposed, taking into account the natural background characteristics of arid basins and prioritizing the comparability of transboundary water quality data. Significant discrepancies between approaches are highlighted. These range from differences in the calculation of composite water pollution indices (e.g., the Water Pollution Index—WPI) and biological indices (e.g., saprobe indices), to inconsistencies in sampling frequency and methods, as well as in the classification of pollution categories. The analysis reveals that the disparity in methodologies hinders the comparability of water quality data even for transboundary rivers, leading to potential disputes between states. The study substantiates the need for harmonizing of water monitoring and assessment approaches, drawing on successful international standards (e.g., the EU Water Framework Directive, US EPA methods, and the CCME WQI). A concept for a unified surface water quality assessment system tailored to the Central Asian region, which accounts for local environmental, sanitary, and political-legal conditions, is proposed.