This paper deals with the state of water supply and the construction of a single water supply system in the area of Varaždin County. Facilitation of water supply installations in surrounding population centres is being considered, and whether enough water can be guaranteed based on current sources of supply and future demand. Introductory consideration is given to natural and social factors affecting the water supply, while most attention is given to demographic elements. The state of the current water supply systems is noted, from traditional sources and small local water supply systems to modern public systems. It has been ascertained that for the needs of the future regional system there are sufficient sources of water with respect to estimated demand, and there are yet untapped and unresearched water reserves. The Varaždin regional water supply system would cover the greater portion of Varaždin County, as well as the town of Sv. Ivan Zelina and Bedenica Municipality, which are part of Zagreb County. The remaining portions of Varaždin County would be covered by two larger water supply systems not directly connected to the Varaždin regional water supply system: the Ivanec and the Bela water supply systems.