Due to sudden changes in hydraulic regime the loose deposits in drinking water distribution systems (DS) lead to discoloration events at the customers tap. About 1/3 of all customer complaints about drinking water quality are due to the discoloration events. The loose deposits may originate from insufficient treatment, microbiological regrowth or corrosion of the pipes. Organic carbon (OC) influences the interaction and transport of many toxic organic or inorganic chemicals found in the nature. The aim of this study was to investigate how the different factors such as the raw water source and the material in the networks influence the concentration of OC in the loose deposits. An OC isolation method for lake sediments was adapted to determine nonpurgeable organic carbon (NPOC) in the loose deposits. The average NPOC amount in deposit samples collected from DS supplied with groundwater varied from 0.18 mg/g to 21.01mg/g. In the samples collected from DS supplied with surface water NPOC ranged from 1.21 to 18.99 mg/g. In samples collected from different drinking water reservoirs in Latvia, NPOC ranged from 0.20 to 3.11mg/g. The pipe material was a single the only important factor influencing the concentration of organic carbon in loose deposits. The smallest average NPOC amount was found in the samples from polyvinyl chloride (PVC) pipes (0.48 mg/g of deposits), while the largest NPOC amount was found in polyethylene (PE) pipes (14.29 mg/g). Samples collected from cast iron (CI) pipes contained 4.64 mg/g. Iron was found to be the dominant material in sediments, followed by silica and aluminum. Goethite and quartz were the minerals which were found in almost all the samples. The OC isolation method was shown to be accurate and simple user-friendly for determination of OC in loose deposits from drinking water.