The Authors carried out a series of researches aiming to control, over time, the state of preservation and the biological properties of a magnesic-calcic-sulfate-bicarbonate medium-mineral water, also available on the market for dietetic purposes. The investigations allowed to demonstrate that when the bottles are opened the pH is stable on the starting values even for bottles opened after more than 400 days from bottling them. It was observed, however, that with bottles which had been left opened for many days, the pH of the older bottles was more stable, while the one of bottles only 50 days old tended to move towards alkaline values and to remain unchanged during the following days. The control of the zymosthenic properties in vitro, with amylase and trypsin on the relative substrates, made possible to demonstrate that the presence of the water under study considerably favours these enzymic processes, which need considerably smaller amounts of enzyme, in comparison with the tests performed on control solutions. Such effect is constantly present even after the water has been bottled for a long time. Tests on loading diuresis on albinic rats showed that the water under study favours a lot the kidney emuntory activity also in not previously treated animals. Animals previously watered with the medium-mineral water, however, in the loading tests with the various waters display a greater functional activity from the kidney "trained kidney". Moreover, the Authors point out that, with such water, the diuretic response seems to be improved of water is drunk after eating.