Prospective invention concerns to area of ecology and analytical chemistry, and also to water treatment, and can be used for estimation the effectiveness of water purification from different origin on water intakes with various stages of technological processing, for assessment of overall performance of filters and water treating devices of household and industrial purpose. The essence of technique consists in use of generalized parameter of total carbon content--technogenic organic carbon--in semi-volatile organic compounds before and after stages of water treatment. The total carbon content is determined by gas chromatography coupled with atomic-emission detection. Due to high sensitivity of method, parameter technogenic organic carbon correctly reflects changes of water quality during water treatment.