The possibility of the bottled natural mineral waters use as a media for keeping of the highly sensitive test-culture of Daphnia magna Straus as alternative to the synthetic medium has been investigated. The mineralization of the considered media varied within 123− 2992 mg/dm 3, Cl-content-11− 1390 mg/dm 3, SO 4 2-− 0.2− 182.0 mg/dm 3, and water hardness 1.8− 3.2 mg-eq/dm 3 (90-160 mg/dm 3 CaCO 3). Maximal fertility (135− 140 juveniles per female over 21 days) were obtained the media of total mineralization within 100− 800 mg/dm 3 and Cl-concentration 10− 25 mg/dm 3. Under these conditions, Daphnia newborns were highly sensitive to the reference toxicant (LC 50 24 1.0− 1.2 mg/dm 3 K 2 Cr 2 O 7), which meets the method validation criteria. In the media where mineralization and Cl-concentration exceeded respectively 1600 and 200 mg/dm 3, fertility rates did not reach acceptable levels. However, the fertility indexes increased after adaptation to these conditions over three parthenogenetic generations. This indicated the high ecological plasticity of D. magna, which can be used to create and maintain cultures for biotesting of waters with a wide range of hydrochemical properties. Thus, if water of appropriate quality is inaccessible, highly sensitive culture of D. magna can be kept in the media prepared of natural mineral water of suitable composition. It can be used as an alternative to the synthetic media and for improvement of the intra-and interlaboratory reproducibility of the bioassay data.