An investigation was carried out to ascertain the effect of drinking Fiuggi water on the microcrystalline structure of the calcium oxalate monohydrate present in urinary sediments provided from patients suffering from recurrent idiopathic oxalic calculosis. The experimental group was administered tap and Fiuggi water for ten days. The control group was administered tap and Fiuggi water according to the same procedure as for the experimental group. The comparative data show that drinking Fiuggi water leads to a strong reduction, and sometimes even to the elimination, of the calcium oxalate monohydrate present in the urinary sediment reducing the risk of oxalic calculosis. Fiuggi water contains organic molecules belonging to the fulvic acid family. These acids are capable of complexing the calcium ions and interact preferentially with the crystal lattice of the calcium oxalate monohydrate via the formation of a film and behave as pumping systems by linking the calcium ion, demolishing the crystal lattice and dissolving calcium and oxalate ions. Mineral water treatments must therefore be viewed as a function of the specific composition of the water administered. The ecosystem influences the composition of water, as a complex matrix containing a number of organic molecules which are potentially biologically active.