The data of 1982–1985 from the Türikoja meteostation (East Estonia) on the isotopic composition of precipitation are generalized and the results compared to those of some European IAEA/WMO network station. The monthly weighted mean value of δ18Ois equal to −10.4‰ and the seasonal isotope gradient ▵δ18O/▵tis 0.32. Thus, in spite of the coastal position of Estonia, the temperature-dependence parameters of precipitation are typical of continental stations. This refers to the insignificant role of the Baltic in the formation of precipitation. The isotope records in Estonian lakes enabled to compile a model based on isotopic balance for a steady-state well-mixed waterbody. The δ18Ovariations in ground-waters mostly fluctuate between −10.8‰ and −12.8‰, but there are aquifers with an isotopic composition considerably different from that of current precipitation, reaching up to −21‰.