Time and spatial variability of the soil water depends on the weather characteristic course, on soil hydrophysical characteristics and on forest stand transformation influence. Analysis of soil water available for plants during the growing season shows that the water dynamics in the soil under the oak forest stand is most intense in the upper (0–50 cm) layers of the soil profile. Water uptake and loss from this soil layer results in transition of the soil water from one category to another, especially due to the osmotic preassure of the soil and the water active transport via fine roots. At the beginning of the growing season capillary movable water category prevails in the soil profile with easy available water supply. Radiation and air temperature increase leads to the gradual decrease of soil water content. Increase of evapotranspiration (> 5 mm.day-1) is folowed by the process of water supply decrease. During the culminating drying off period (July, August) the soil water supply decreases to the category of capillary immovable water. During extremely dry season the water supply in the soil can decrease to the wilting point level. Soil water becomes capillary bound and non-available for plants. Loss of contact between the fine roots and water results in decrease of transpiration and assimilation. Premature fall off of physiologically weakened leaves is recorded. Under such conditions the oak resistance towards damaging factors is decreased.