Raw water in Latvia contains high concentration of natural organic matter which causes large amount of bacteria in drinking water distribution system. The aim of this study was to decrease organic carbon (OC) concentration in humic rich drinking water using membrane bioreactor (MBR) and describe biomass growth kinetics. The lab-scale study was carried out and changes of total organic carbon (TOC), dissolved organic carbon (DOC), concentration of bacteria in MBR were measured. To get results MBR should reach steady-state level and with definite parameters like temperature, inflow and air concentration were controlled. Inlet water has taken from distribution network and it has concentration of TOC 9,20±2,98 mg/L and DOC 8,15±1,98 mg/L and after MBR processes reached respectively 9,7% and 8,94% decrease. The concentration of BDOC decreased in MBR for 61.22%. Results showed that amount of cells in MBR are close connected to temperature changes in reactor and number of cells in outlet water. This observation could be explained with biomass sorption on biomass elements, which after 32 d experiment was 7.7E+8cells/cm2.