The necessity of rational water resource management and reduction of water consumption demandsthat water utilities address water losses during water treatment. Therefore, the backwash water generated during the filtration process is often the focus of research aimed at its reuse within the water treatment system. The studies outlined here were conducted in a large water treatment plant (100,000 m3), focusing on the backwash water produced from sand bed filter flushing. Prior to its reintroduction into the treatment train, the backwash water underwent pre-treatment using ultrafiltration (UF) process with two different modules: a spiral module with a PVFD (200kDa) membrane and a capillary module with a PES (80kDa) membrane. The effectiveness of the process was evaluated based on the degree of retention of organic substances and microorganisms, which pose health risks in backwash water recirculation. The capillary membrane exhibited greater effectiveness in retaining these contaminants, thereby ensuring the complete elimination of pathogenic microorganisms. The study findings indicate that pre-treating backwash water using UF membranes and reintroducing it into the water treatment system before the ozonation process can lead to a reduction of environmental fees. However, this process results in a 1.5% increase in water treatment costs

The results of the first limnological studies of the Kuźnica Warężyńska anthropogenic reservoir, by flooding the sand mine excavation, in 2005, are presented. Measurements of water temperature and the concentration of oxygen dissolved in water were made every month, from April to December, every 1 meter deep from the surface to the bottom (22m). Kuźnica Warężyńska anthropogenic lake was classified according to Olszewski and Patalas as dimictic, eumictic, stratified, stable, and extremely limnic. In terms of the share of the littoral zone in the total area, the reservoir is classified as grade II according to Dołgoff, where the pelagic zone is similar to the littoral zone. After 14 years of the reservoir's existence, during the summer stagnation period, the oxygen in the hypolimnion is completely depleted, from the 10th meter deep to the bottom, 22m. The analysis of the vertical distribution of the regression coefficient for the relationship between water temperature and the concentration of dissolved oxygen in water indicates the influence of the oxygen-free groundwater supplying the reservoir as a factor that may, in addition to the decomposition of organic matter, initiate anaerobic processes in the bottom water layer of the reservoir. When circulation ceases, the bottom eruption of oxygen-depleted groundwater is, during the summer and winter stagnation, a factor that shapes the anaerobic environment in the bottom layers of water early, initiating the internal enrichment process. Hydrological conditions, morphometry and thermal-oxygen relations of the Kuźnica Warężyńska reservoir are favorable for undertaking technical measures - changing the method of draining water from the surface to the bottom - to protect the quality of water resources.