The results of long-term investigations into the post-Chernobyl period of radiocesium activity concentrations in cistern waters along the Croatian coast of the Adriatic Sea are presented. The 137 Cs activity concentrations in cistern water samples were in excellent correlation with fallout activities. The observed mean residence time of 137 Cs in cistern waters was estimated to be 6.9±0.8 y. Cesium-137 radioecological sensitivity for the period 1988–1997 for cistern water was estimated to be 1.17× 10− 3 Bq y− 1 L− 1/(Bq m− 2). The annual total effective dose incurred by 134 Cs and 137 Cs that a hypothetical adult person drinking 1 L of cistern water per day would receive was estimated to be< 1 mSv in 1986, decreasing to 3.6 μSv in 2015.