Water losses are an integral part of all water supply systems. They represent the difference between the affected and the delivered water. According to the size and detecting possibilities, water losses are divided into large reported leakage, lesser unreported leakage and the slightest background leakage. Commonly accepted methodology to reduce losses has been developed by the International Water Association – IWA and it’s applied as follows: the first step is the preparation of the water balance in order to determine the size and types of losses, Infrastructure Leakage Index – ILI and economically acceptable level of leakage - ELL. After preparation and determining the water losses, it's necessary to apply a strategy for water leakage reduction and to determine reduction methods, depending on the options and parameters of the water supply system, the size of losses and other parameters. In this thesis, the methods for reduction of water losses by pressure control and active leakage control are discussed. Pressure control represents a reduction of pressure in all parts of the system where it's possible without negative influence on technical requirements and on supplying the consumers. Pressure control has the biggest influence for reduction of small background leakage. Those leaks are plentiful, and their detection and repair is not cost-effective. By controlling the pressure, total losses of such leakage can be reduced by more than 50%. Active leakage control assumes rapid and intensive leakage detection and repair on the field. Locating leaks can be implemented in various ways. The most commonly used are acoustic methods (correlators, geophones, “Smart Ball” ...), but there are other alternative non-acoustic methods such as ground penetrating radar - GPR, gas injection into the system, infrared thermography and others. All the methods are discussed later in this thesis. It is recommended to use at least two methods during active leakage control in order to determine location of the leak with greater certainty. In the last section of the study, there is detailed practical example of the application and results of active leakage on JANAF water supply system of oil terminal „Omišalj“.