There are no mineral resources of wider importance in the area of ​​Leżajsk. Sand deposits, clay gravels are of local importance. Undoubtedly, the largest source of natural material are the inexhaustible sources of artesian water. The proximity of a large, water-rich river allows you to meet the water needs of the city, industry and agriculture. These sources decided, among others, about the location of some industrial plants.

Oligocene water is artesian water, located between two layers of rock and drawn from the so-called Oligocene wells. The name of the water comes from medium and coarse oligocene glauconite sands, occurring at a depth of about 200 meters.

Groundwater being the basic source of supply is shallow, but the efficiency of economic wells varies. Potable underground water reservoirs are found in river alluvia in the San Valley. In the upland areas, ground waters occur at a depth of about 2-4 m, in deep dune areas they lie much deeper, up to 10 m.

These are most often surface water with large fluctuations in the level of the mirror, strongly reacting to precipitation. Overhead water supplies periodic waterways that dry up in the autumn. To the south of Leżajsk, in the area of ​​sand-dust deposits, groundwater is deep, often below 20 meters from the surface. These are waters with very favorable physicochemical parameters. The waters of the deeper ground are included in the Miocene formations and are usually unsuitable for economic purposes due to the high content of chlorides, sulphates, iron and manganese.