<p>This study investigates the occurrence and distribution of Radon-222 (²²²Rn) in groundwater, Tigris River water, and tap water in the Al-Baitha area, southeast of Baghdad, where local communities rely heavily on groundwater for drinking and irrigation purposes. A total of 21water samples (15 groundwater, 3 river, 3 tap water samples) were analyzed using a RAD7 detector, along with measurements of δ¹⁸O isotopes, pH, well depth, and total dissolved solids (TDS).The results indicate that ²²²Rn concentrations in groundwater ranged between 6.79 and 14.41&#xa0;Bq/L, exceeding the U.S. EPA guideline value 11.1&#xa0;Bq/L at several locations, particularly in wells located farther from the Tigris River. Radon concentrations were positively correlated with TDS and distance from the nearest river, whereas pH and well depth showed no statistically significant influence. Oxygen-18 isotope signatures indicate that groundwater recharge is primarily derived from the Tigris River, with isotopic enrichment reflected as less negative δ¹⁸O values in distant wells, consistent with longer groundwater flow paths and enhanced radon accumulation .The estimated annual effective doses ranged from 17 to 37 µSvy^-1 for ingestion and from 17 to 36 µSvy^-1 for inhalation, while river and tap water doses 4 to 5 µSvy^-1 remained well below the WHO recommended limit 100 µSvy^-1. These results highlight the importance of systematic groundwater monitoring and underscore the role of hydrogeological factors in controlling radon accumulation in groundwater systems.</p>