Relevance. The article presents comprehensive studies of water loss assessment in the internal water supply networks. In order to increase the practical value of the studies, in a number of settlements of the Republic of Armenia, systems of internal water supply networks with different technical conditions (number of floors, amount of pressure in the network, year of construction, type of gauging device, etc.) were selected. In terms of these conditions the loss assessment analyses were implemented, taking into account the local conditions. The paper introduces the proposals aimed at reducing the volumes of unaccounted water amounts. Aim. Based on the importance of the issue, we have carried out assessment studies of the loss components of the system, as the correct assessment is important for increasing the efficiency of detection of general leakages of the water supply system. Water balance of the settlements was developed, based on the loss assessment studies carried out in the original conditions and the structure of the housing stock. In the work aimed at increasing the efficiency of water supply system, it became clear that the correct assessment of the components of losses leads to the systematic execution of targeted actions of discovering the loss of the system and their recovery, as well as the development of a road map of reconstruction processes. Objects. Water balance supplied for drinking and economic purposes, as well as the components of supplied water. Methods. Well-known hydraulic principles and laws. Experimental studies were conducted directly on the water supply network while it is operating. Results. The studies carried out in different settlements show that the unaccounted water amount in the internal water supply network is almost equal to the volume of the sold water amount. In the system which has 71.4% water loss, unaccounted water volume caused by low accuracy of water meters and the emergency condition of internal networks of private houses is over 27.7%.