The water supply of the localities in the Ilişua drainage basin. The way in which the water is supplied to a locality represents a relevant indicator in assessing the quality of life and the economic development. The existence of a well developed water supply system is all the more necessary as the spatial-temporal distribution of the rainfall undergoes an enhancement of variation together with the increase of water requirement.The 27 localities located in the drainage basin, with a population of more than 13,000 inhabitants, engaged mostly in primary activities need a water supply system with a quality source and a sufficient flow to induce an actual immunity in the context of present climate changes. In order to achieve this goal, one has to consider calculating the water requirement, analyzing the territory natural component in order to make possible the identification of the water supply sources and of the water uses territorial distribution.