Abstract Rain floods are frequent for mountainous rivers of Georgia. As a reason of the recent floods and high waters the norms of maximum water discharge, its extreme and probable values have been ascertained. These norms are vital for planning organizations for safety of various constructions. The territory of Georgia is divided into different regions according to various types of high water rates, which enable to predict the flow of yet unstudied rivers. For the same purpose, regional equation considering sub watershed areas and average annual water expenditure has been worked out. Applying multifactor statistical model, prognostic equations with various factors have been detailed for maximum water discharges 1-3 months beforehand and rain floods 1-2 days advance. The prognosis is ascertained constantly considering precipitation, air temperature, liquid water content of snow and rivers. When high water peaks are expected appropriate measures have to be carried out in advance for safety of population, economy and environment.