[en] A mobile purifying plant for drinking water was tested for its usability in the case of radioactive contaminated water. As radioactive pollution the isotopes ⁸⁹Sr, ¹³¹I, ¹³⁴Cs and ¹⁴⁰Ba/¹⁴⁰La were chosen. The tests were made in a 1 : 1000 scaled-down version in a laboratory. Subsequqent a large-scale test was made with the purifying plant to control the results of the laboratory tests. The investigations have ensured the following purifying factors RF (in paranthesis the values of the large-scale test): ⁸⁹Sr: RF = 7.8-11.4 (3.4), ¹³¹I: RF = 6.5-7.1 (1.74-2.05), ¹³⁴Cs: RF = 184-260, ¹⁴⁰Ba: RF 92-97, ¹⁴⁰La: RF>= 103. An estimation of the radioactive contamination of the water by an accident of a medium nuclear power plant gives a purifying factor RF>=100 for all radiosiotopes to supply the population with drinking water. Because the RF of ⁸⁹Sr and ¹³¹I are far beyond this limit the tested mobile purifying plant for drinking water cannot be used in the case of radioactive contaminated water. (author)