A new monitoring system has been established to assess low-level radioactive caesium in Fukushima waters directly using caesium adsorbents: plastic containers, U8 containers, and a germanium (Ge) detector container packed with nanoparticle-Prussian blue (PB) immobilized on a polymer. The results show that the calibration coefficient for a flow rate of 0.3 L min(-1) was 1.27 in Fukushima waters for germanium semiconductor scintillations related to (133)Cs concentrations and radioactive caesium amounts.