Background: Radium-226 (²²⁶Ra) is a product of the ²³⁸U radionuclide decay series that significantly incorporated into the human body through water intake. It can also potentially cause a series of health problems including cancers of the digestive system. Radium-226 (²²⁶Ra) is a product of the ²³⁸U radionuclide decay series that significantly incorporated into the human body through water intake. It can also potentially cause a series of health problems including cancers of the digestive system. Materials and Methods: ²²⁶Ra has been determined in drinking water samples collected from various locations of Guilan province of Iran. The water samples are taken from public water and urban tap water sources. For evolution of gross a and b exposure precipitation method and proportional scintillator system was used. The radon emanation method was used to measure the radium concentration in drinking water. Results: The measurements showed the gross α and β concentration ranges were between <38 mBql^-1 to 92 mBql^-1 and <41 mBql^-1 to 328 mBql^-1, respectively. The radium concentration range was between 2 mBq l^-1 to 38.2 mBq l^-1. The resulting contribution to the annual effective dose due to the digestion of ²²⁶R in water was calculated to be between <0.4 μSv y^-1 to 7.8 μSv y^-1, respectively. Conclusion: The average concentration of ²²⁶Ra was found (7.6 mBq l^-1) in drinking water samples and the average annual effective dose, from the digestion of ²²⁶Ra in water samples was calculated to be 1.5 µSv y^-1. According to UNSCEAR, the annual effective dose value by ingestion is report to be 0.12 mSv y^-1.