This paper reports the estimation of the radiation doses in the human body in the Ebro river basin (Northeast Spain), following drinking water ingestion by measuring 40K, 226Ra, 90Sr and 3H. The equivalent dose in ten different organs was estimated. Dose calculations were performed by means of the GENII computer program. The lowest equivalent dose calculated through ingesting drinking water was in the small intestine whereas the highest was in the bone surface. Copyright © 2006 Inderscience Enterprises Ltd.