A total of 107 potable water samples were collected from various rural and urban sources located in the Lublin region (eastern Poland). 54 samples from rural sources comprised 32 samples of untreated well water and 22 samples of treated (chlorinated) tap water from rural dwellings distributed by the municipal water supply system (MWSS). 53 samples of treated water from urban sources were supplied by the city of Lublin MWSS. They comprised: 11 samples of tap water from offices and shops, 8 samples of tap water from dwellings, 19 samples from showerheads in health care units, and 15 samples from the outlets of medical appliances used for hydrotherapy in a rehabilitation centre. Water samples were examined for the presence and species composition of Legionella, Yersinia, Gram-negative bacteria belonging to family Enterobacteriaceae (GNB-E) and Gram-negative bacteria not belonging to family Enterobacteriaceae (GNB-NE), by filtering through cellulose filters and culture on respectively GVPC, CIN, EMB and tryptic soya agar media. Legionella was recovered from samples of well water, tap water from rural dwellings, tap water from urban dwellings, and water from medical appliances - with the isolation frequency of 27.8-50.0%, and the low concentrations ranging from 0.7-13.3 × 10¹ cfu/l. No Legionella strains were detected in tap water from offices and shops, and in water from showerheads in health care units. Strains of the Legionella pneumophila types 2-14 predominated, forming 89.9% of total Legionella isolates, while other species of Legionella formed 10.1%. Neither Legionella pneumophila type 1 strains nor Yersinia strains were isolated from the examined water samples. The isolation frequency and mean concentration of GNB-E in water samples from rural sources was significantly greater than in water samples from urban sources (respectively 61.1% vs. 20.8%, 17.1 vs. 3.4 × 10¹ cfu/l, p<0.001). Isolation frequency of GNB-NE in water samples from rural sources was significantly greater compared to that from urban sources (77.8% vs. 47.2%, p<0.01), but there was no significant difference in the concentration of GNB-NE in both sample sets. A significant correlation was found between concentrations of Legionella and GNB-NE for total MWSS water samples (p<0.001), but not for the total well water samples. Altogether 34 GNB-E and GNB-NE species and/or genera were identified in the examined samples, out of which 21 were potentially pathogenic. Enterobacter spp., Klebsiella spp., Serratia spp., and Pantoea agglomerans were most common among GNB-E, while Acinetobacter spp. and species of Pseudomonadaceae family predominated among GNB-NE.