Graphical Abstract: The aim of the study was to modify the diatomite from Ghidirim village (Ribnita distinct, Republic of Moldova) with purpose to use it as filter material. The initial diatomite was modified by alkaline treatment with sodium carbonate, and the filtering capacity was evaluated by suction filtration method. The treatment of diatomite by sodium carbonate resulted in an increased filtration rate, recording the most pronounced filtering capacity for diatomite treated with 20% solution of sodium carbonate.