QUALITY CRITERIA OF NATURAL WATERS: CHEMICAL ASPECTS OF USE IN IRRIGATION AND FERTIGATION (A CASE STUDY OF MOHYLIV-PODILSKYI DISTRICT, VINNYTSIA REGION)

A study of water bodies in the Mohyliv-Podilskyi district of the Vinnytsia region was conducted to assess the suitability of water for irrigation purposes. The research covered local water sources, including surface water, catchment systems, a pond, and the Kotlubaivka and Dniester rivers (both upstream and downstream of wastewater treatment facilities). The analyses were conducted in a certified laboratory at the National University of Life and Environmental Sciences of Ukraine. The research included an assessment of the chemical composition of water in terms of macro- and microelements, as well as quality parameters such as pH, mineralization, and temperature. Analytical and statistical methods were used, along with calculating water quality indicators such as SAR (Sodium Adsorption Ratio), Stebler’s irrigation coefficient A, and the Water Quality Index (WQI) using the Harrington function. Significant fluctuations were observed in the concentrations of cations (Na⁺, Ca²⁺, Mg²⁺), anions (Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻), and heavy metals (Cd2+, Zn2+, Pb2+, Cu2+, Fe2+), some of which approached maximum permissible concentrations. It was found that, according to the SAR index, sources No. 2 and 5 demonstrated the highest water quality, while source No. 6 was deemed unsuitable due to the risk of soil salinization. The empirical irrigation coefficient A confirmed good to satisfactory water quality for most sources, except for sources No. 6 and 8. According to the Harrington water quality index, the most favorable source was the Dniester River (No. 7) upstream of the treatment facilities (59.9 %), with sources No. 2 and 5 serving as alternative options. The obtained results support the relevance of applying integrated assessment approaches for determining water suitability for irrigation and fertigation, taking into account chemical composition, environmental risks, and technical feasibility. The findings form a basis for future sustainable water use and environmental monitoring measures.