The quality and usability of water flowing out of the Korzeń stream catchment were assessed in order to determine whether it can be stored in a small retention reservoir. The Korzeń stream catchment (9.65 km²) is situated in the Tarnów county, in the hypsometric range of 231 to 397 m a.s.l. The investigations were conducted from January 2005 to December 2006. Water was sampled once a month. Temperature, pH, concentration of dissolved oxygen, degree of oxygen saturation, and electrolytic conductivity were measured on site, while total suspended solids, phosphates (PO₄^3–), ammonia(NH₄⁺) nitrites (NO₂^–), nitrates (NO₃^–), dissolved solids, sulphates (SO₄^2-), chlorides (Cl^-), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), total iron (Fe^2+/3+) and manganese (Mn²⁺), as well as BOD₅ (only in 2006) were determined in a laboratory. In terms of total suspended solids, iron and manganese concentrations, the water flowing out of the catchment may be classified into the 3rd class of water purity, i.e. into the waters with satisfactory quality. In terms of manganese concentrations, the water from the Korzeń stream would be fit for consumption only after a highly efficient physical and chemical treatment. Nitrites are the main component that adversely affects the living conditions of fish, whereas total suspended solids and water oxygen saturation sporadically do not meet the quality criteria for bathing water.

In the years 1999–2001, research was conducted on the hydrological conditions of a small sub-mountain catchment of the Włosień stream situated in the Wieprz district in the Wilamowickie Foothills mezoregion. Almost 80% of the catchment is used for agriculture, and about 16% is covered by forests. With respect to precipitation, the research period may be considered as average because the mean annual precipitation was 912 mm which constituted 105% of the multi-annual mean. However, the individual years differed considerably in precipitation amounts: the first year was dry, the second year was normal, while the third year was very wet. The mean annual temperature of air, 9.0^oC, was by 1.2^oC higher than the multi-annual mean. Under such conditions, the annual depths of outflow layers ranged from 305 to 512 mm. On average, the outflow layer was deeper in the summer half-year due to the extremely large July outflows in the two last years of research. Despite the varied meteorological conditions, the outflow coefficients in individual years were almost identical and constituted 44% of the precipitation, on average.

The quality and usability of water in the Wilga River water were assessed in order to determine whether it can be stored in a projected small retention reservoir. The Wilga catchment up to the gauging section under study has an area of 19.67 km2 and is situated in the Wieliczka county (Małopolska province). Hydrochemical studies were carried out from March 2006 to February 2007. Water temperature, pH, dissolved oxygen concentration and conductivity were measured on site, whereas total suspended solids, total dissolved substances, biogenic compounds (NH⁺, NO₂^–, NO₃ ^- , PO₄ ^3–) and mineral constituents (SO₄ ^2–, Cl^–, Mn²⁺, Fe^2+/3+, Mg²⁺, Ca²⁺) were determined in a laboratory. In terms of nitrate, iron and manganese concentrations, the Wilga River water flowing out of the catchment was classified into the 3rd purity class, i.e. into the waters of satisfactory quality. The projected reservoir may serve recreational purposes because the water fulfills the requirements posed for bathing sites. After a typical physical and chemical treatment it may also be used to provide water supply for the local community (category A2). Because of very high nitrite concentrations, however, the water creates an unsuitable environment for fish to live in.

The relationship between the load of pollutants delivered to a vertical-flow sand filter on the load removed by the filter was studied using the data from four household sewage treatment plants consisting of a septic tank and a vertical-flow sand filter, investigated from October 2003 to February 2006. The pollutant load carried by sewage was determined on the basis of the amount of sewage coming to a treatment plant and the values of BOD₅, COD_Cr, suspended solids, total nitrogen, and phosphates in pretreated and in treated sewage. There was a very high correlation between the pollutant load entering the filter bed and the load retained in the bed, especially for BOD₅ (r = 0.99), COD_Cr (r = 0.98), total suspended solids (r = 0.93), and total nitrogen (r = 0.98), whereas for phosphates the relationship between the two factors was weak (r = 0.27).

To determine the degree to which tap water gets contaminated during its use and to assess the effectiveness of treatment of the sewage produced from this water, the mean values of some indicators and components of contamination were compared in raw sewage, in sewage leaving the mechanical-biological treatment plant, and in tap water. The work examined also the composition of sewage sludge and investigated the effect of the sewage on the receiving body and the environment. It was found that the ammonium nitrogen content of treated sewage was lower than that of drinking water. The results on total nitrogen showed that the amount of this component in the receiving body was three times higher than its amount in treated sewage, which, however, is practically impossible. Similar inconsistencies between the data on sewage and those on water in the river being its receiving body occurred for phosphorus and total suspended solids, which may indicate that the study methods employed in practice are inaccurate. Comparison of the results on the amount and quality of raw sewage, treated sewage, sludge, and water of the receiving body points to the conclusion that the existing method for determining the effectiveness of sewage treatment is inappropriate. It is suggested that the monitoring of the sewage treatment effectiveness of a treatment plant should be based on the balance of components in treated sewage and in sewage sludge.