[en] TENAWA project (Treatment Techniques for Removing Natural Radionuclides from Drinking Water) was carried out on a cost-shared basic with the European Commission (CEC) under the supervision of Directorate-General XII, Radiation Protection Unit. TENAWA project was started because in several European countries ground water supplies may contain high amounts of natural radionuclides. During the project both laboratory and field research was performed in order to test the applicability of different equipment and techniques for removing natural radionuclides from drinking water. The measurable objectives of the project were: to give recommendations on the most suitable methods for removing radon (²²²Rn), uranium (^238,234U), radium (²²⁶, ²²⁸Ra), lead (²¹⁰Pb) and polonium (²¹⁰Po) from drinking water of different qualities (i.e. soft, hard, iron-, manganese- and humus-rich, acidic) to test commercially available equipment for its ability to remove radionuclides; to find new materials, absorbents and membranes effective in the removal of radionuclides and to issue guidelines for the treatment and disposal of radioactive wastes produced in water treatment. Radon could be removed efficiently (>95%) from domestic water supplies by both aeration and granular activated carbon (GAC) filtration. Defects in technical reliability or radon removal efficiency were observed in some aerators. The significant drawback of GAC filtration was the elevated gamma dose rates (up to 120 μSv/h) near the filter and the radioactivity of spent GAC. Aeration was found to be a suitable method for removing radon at waterworks, too. The removal efficiencies at waterworks where the aeration process was designed to remove radon or carbon dioxide were 67-99%. If the aeration process was properly designed, removal efficiencies higher than 95% could be attained. Uranium could best be removed (>95%) with strong basic anion exchange resins and radium by applying strong acidic cation exchange resins. Also, weak acidic cation resin, zeolite A, sodium titanate and manganese dioxide were found efficient in radium removal. Hydroxyapatite removed both uranium and radium. Simultaneous removal (>95%) of uranium, radium, lead and polonium could be carried out by nanofiltration and reverse osmosis. The side-effect of RO-technique was the quality of the effluent; the water becomes almost totally demineralised and therefore corrosive. Commercially available iron and manganese removal equipment removed variable amounts of radon (0-90%), uranium, radium, lead and polonium (0-100%) depending on the operation principle. Lead and polonium could be removed only fairly well by ion exchange and GAC filtration (35-100%). The presence of lead and polonium in particles of different sizes in groundwater was determined in the laboratory. Only in one type of water, with relatively high NaCl concentration and rich in humus material, was a considerable fraction, about 20%, of both radionuclides found to be present in the soluble form. In the other types of water only from 1 to 2 % of lead and polonium was soluble. It is expected that neither lead nor, especially polonium would form intrinsic precipitates but they would be adsorbed on colloidal minerals and organics. When different kinds of treatment methods are used to remove natural radioactivity from drinking water, wastes containing natural radioactivity will be produced. It is recommended that the annual dose to inhabitants from external gamma radiation of a GAC filter should not exceed 0.1 mSv. It is also recommended that the dose rate at a distance of 1 m from the GAC filter should not exceed 1 μSv/h. To achieve these aims the GAC filter should be equipped with special shielding to attenuate gamma radiation. It is also recommended that the wastes containing natural radioactivity in solid form be discharged into communal dumps, and wastes containing natural radioactivity in liquid form be discharged into the sewer. (orig.)