The accidental release of large quantities of radionuclide after a nuclear accident tends to contaminate the groundwater system or rivers and lakes by the transfer of the main radionuclides such as Cesium 137, Strontium 90 or Cobalt 60, Ruthenium 106 and others (including transuranic radionuclides, such as: 239-Pu, 240-Pu, 241-Am...). The aim of this paper is to review the possible solutions for the removal of these contaminants from large quantities of water. i) The use of crown ethers for the selective removal of Strontium 90 such as the dicyclohexyl 18-crown 6 which is able to remove with 90% of efficiency the Strontium. ii) The use of zeolithes for the removal of Cesium 137. On larger scale the use of electromagnetic filtration technology is able to process in a relatively short time large quantities of water by using a seeding system of resin coated metallic magnetic particles to enhance the filtering efficiency under cold conditions. Examples of water of efficiencies and results obtained on loops at a fairly large scale will be given in this paper, these examples show rather high efficiency of removal even at low concentration of contaminants (a few ppb: part per billion). Examples of water treatment concepts will be also given for treatment of contaminated surface water and to treat large groundwater applications. Major applications could be implemented on various sites namely in Russia (Karatchai Lake) or in Belarus and Ukraine. The magnetic filtration is not a new concept but with the use of various selective adsorbing treatment particles, this concept has been proven so effective that dissolved metals in process water have been reduced to level in the very low ppb range.