An analysis of climatic water balances in Wrocław was performed for the period of 1881 - 1992 and revealed a very high variability in annual sums, as well as a suggestion of their periodicity. On the basis of measurement data of the University of Agriculture Observatory covering the period of 1961 - 1992, very strong variability of climatic water balances was shown, particularly in the summer half-year, and a tendency towards increasing water deficiency. On the basis of a series of over 100 years of observations, it is possible to suggest an improvement in water relations. Extreme values and their distributions will form the basis for a model of long-term variations in the natural hydrological cycle. Indispensable here are studies on the effect of atmospheric contamination and chemicalization of agriculture on evapotranspiration, the level of which can cause significant changes in soil moisture, water outflow, and water quality.