Aim of the study:
The paper presents calculations of the filtration through the side dam of the "Maziarnia" water reservoir in Wilcza Wola in the Podkarpackie Voivodeship.

Material and methods:
In the selected sections, on the basis of penetration drilling and research excavations, the geotechnical structure of the dam body and base was identified and the samples for laboratory tests were taken. The results of the tests and calculations of the soil filtration coefficient of the dam body were used for the calculation of unsteady and steady filtration through the dam using the finite element method in the GEO5 software.

Results and conclusions:
The analysis of the results showed differences in the filtration coefficient values obtained from laboratory tests and calculated using empirical formulas as well as a relatively good compatibility of the position of computational filtration curve through the dam with the curve resuting from piezometric measurements.