The European Union Water Framework Directive obliges each country to monitor the groundwater level as it is an important source of drinking water, but also an important part of agriculture. A water budget is used for assessing the accuracy of the groundwater level determination. The computations of the water budget are based on evapotranspiration and the state of land surface hydrosphere. On the basis of the determined water budget, statistics and the prognosis for the next 12 months can be computed. In this paper, all the components of the water budget, such as precipitation, surface run-off and evapotranspiration, are studied for the three tested locations in Poland: Suwalki, Zegrzynski and Tarnow cells. The resultant water budget was also determined and presented graphically. On the basis of the water budget research, a prognosis was determined using AutoRegressive Integrated Moving Average (ARIMA) models with the parameters (2,0,2). A comparison between actual water budget data and a prediction prepared for 2015.08–2016.08 indicated that analysing a 12-month period provides a satisfactory prediction assessment.