It was established that the exceedances (ratio) of the concentrations of the indices in the Biological wastewater treatment plant (BTP) downstream / upstream of BTP indices occur practically for all the pollutants analyzed, especially for NH4+ of 7.05 times, BOD5 of 4.22 times, COD-Cr of 4.77 time. The ratio of the concentrations of the analyzed indices from the waters, out of the BTP / norms established by GD 950 of 25.11.2013, (Annex 2), for the analyzed pollutants took place, for: substances in suspension in the interval 1.16-1.77 times; COD-Cr, overruns are 2.36-4.77; for BOD5, in the range 1.46-2.40; after NH4+, the value of the ratio is in the range of 2.13 - 10.64 times. The largest exceedances, as for the ratio of the concentrations of the indices in the downstream BTP/ upstream BTP waters, as well as for the ratio of exit from BTP/ GD 950 norms of 25.11.2013, (Annex 2), in the first place are the exceedances for NH4+, followed by the exceedances for BOD5, COD-Cr and suspended substances. The results confirm that the treated water at BTP Floresti, as in the cases of urban ecosystems Chisinau, Orhei, Telenesti, Balti, is one of the essential sources of surface water pollution.