In the Busko and Solec Spas, saline sulphide and sulphate waters are exploited at different depths. The shallow water system in Busko is related to an interglacial or interstadial period shown by the lack of tritium and¹⁴C and its δ¹⁸O and δD values equal to that of modern water. The noble gas temperatures (NGT) are somewhat lower than the present air temperatures, but the⁴He and⁴⁰Ar ages of about 90–480 ka confirm a Pleistocene recharge. The δ¹⁸O and δD values of the deep system are much heavier than those of local modern waters, which may mean the recharge of a warm pre-Quaternary climate. The⁴He,⁴⁰Ar and²¹Ne contents and the NGT values confirm the deep system to be recharged at the pre-Quaternary stages of the present hydrologic cycle, i.e. after the sea transgression in the Badenian. High SO₄²⁻ contents indicate that the Cl⁻ and SO₄²⁻ in both systems originated from simultaneous leaching of NaCl and gypsum. Other components can be explained by cation exchange between water and Badenian clay minerals in marls (e.g. Ca²⁺ for Mg²⁺ and Na⁺ for K⁺) and by the decay of marine organic matter supplying Br⁻, I⁻ and B.