Introduction. The availability in Ukraine of diversified unique natural mineral water (MW) resources does necessitate a detailed study of that water properties in order of its widespread use in the balneological and extra-resort practice, considering the MW as an important factor of population health preserving and improving [1]. The mineral water rational use is largely determined by its physical and chemical composition, sanitary and microbiological status, the presence of autochthonous microorganisms and those microorganisms’ ability to influence the water organoleptic characteristics and biological properties. In MW practical use the key importance is tribute to controlling the water quality parameters for the prediction of water safety degree and the detection of biological exposure. The MW biological effect depends on the mineralization degree, chemical composition, presence of biologically active components and compounds, as well as on their microbial cenosis’ metabolic products. Analyzing the mineral water microorganisms’ list we reveal their active biochemical effect [1]. The numerous microorganisms contributing to the mineral water’s autochthonous microflora do often include significant concentrations in saprophytic microorganisms producing the catalase as an enzyme of oxidoreductases class, a heme-containing chromoproteid making part of the cell’s antioxidant system and acting as an antiperoxidant protector agent [2]. Peroxide mechanisms may occur in the brain and in other tissues during aging, when exposure to poisons and toxins, when cerebral apoplexy, at nervous system injuries, and others processes. The biological role of catalase refers to the complex enzymatic protection of cell membranes against hydrogen peroxide-caused degradation. The catalase does metabolize the hydrogen peroxide, preventing its accumulation in the cell through producing water and oxygen. The most relevant catalase application relates to the treatment of diseases requiring an effective antioxidant protector: cardiovascular, rheumatic diseases, allergies, central and autonomic nervous systems’ diseases, gastrointestinal diseases, oncology, plastic surgery, etc. [2]. Given the important physiological role of catalase, it is necessary to determine the mineral water’s enzymatic activity. At present the methodology for MW enzymatic activity determination is still absent, so such methods’ elaboration problem is top priority one. Analysis of recent researches and publications. Methods for catalase activity quantitative determination are based on the estimation of enzyme-cleaved hydrogen peroxide quantity when enzymatic activity is assessed by the catalase index. The reference sources describe several methods of catalase activity assessment, but these methods relate to the biological objects (plasma, serum, etc.). To develop methods for determining the MW catalase activity we proceed to review the available approaches. Known is the enzymatic activity determining method by Bach and Oparin based onto titration [3], through assessing the quantity of hydrogen peroxide decomposed during incubation with the enzyme. The amount of hydrogen peroxide in the reaction mixture is assessed by titration with a Potassium permanganate solution in an acidic environment. However, this method has such drawbacks as a high labour intensity, results’ poor reproducibility and low sensitivity.