An alpha spectrometric method for the rapid determination of 226Ra isotope in water samples is presented. The method is based on the co-precipitation of (Ba)(Ra)SO4 for source preparation. The parameters contributing to the uncertainty budget are investigated. Geometry factor (solid angle / 4π) was used instead of 226Ra standard disc for the determination of detector efficiency. The analytical method has been successfully applied to the determination of 226Ra for water samples in proficiency tests organized by International Atomic Energy Agency (IAEA) and National Physical Laboratory (NPL). The proposed method also showed high reproducibility.