The article deals with the optimization of pressure conditions in public water supply systems. By reducing the pressure in the water supply system, the reduce of the direct losses of water from the supply system will be reliably achieved, on the other hand there is also a slight decrease in water consumption in the connected properties. Consumption is possible to divide into two parts that are pressure and non-pressure dependent consumption. The quantification of the impact of a pressure reduction in the water supply system is not trivial. In order to achieve the optimal pressure conditions in the water supply system, it is necessary to consider what pressure should be achieved in the outcome so as to achieve an economic optimum while maintaining the basic limiting conditions, i.e. the adherence to the required pressure conditions in the water supply system at the connection point. These tasks are typically solved using simulation software tools, e.g. on the basis of EPANET. However, there is still a lack of much relevant information to enter into this analysis and subsequent decision making. Within the present study, a long-term experiment was carried out, where a very precise measurement of pressures and flows in the internal water supply of the administrative building was carried out. Different water pressures were set at the inlet point of the internal water supply of the building at fourteen-day time intervals, and the volumes of consumed water were measured at the same time. The obtained data were statistically evaluated. The dependency between the decrease respectively the increase of the pressure in the internal water supply and the water consumption was monitored. The article offers very interesting results.