Bacterium Acinetobacter baumannii is an emergent pathogen associated with nosocomial infections, which can be also found in natural waters. The impact of ecological factors on A. baumannii is insufficiently investigated. The aim was to examine the influence of temperatures (−20 to 80 °C) and pH values (2 to 12) on the survival of environmental and clinical isolates of A. baumannii in nutrient-deprived spring water (SW) and nutrient-rich diluted nutrient broth during 5 months. A. baumannii successfully survived at −20 to 44 °C and neutral pH for 5 months, which is consistent with the persistence of this pathogen in the hospital environment. At temperatures 50 to 80 °C the survival of A. baumannii ranged from 5 days to 5 min. The pH 2 was the most lethal with survival time up to 3 hours, suggesting that acidic conditions are promising for disinfection of water contaminated with A. baumannii. Although the type of media was not statistically significant for long-time survival, the extensively resistant or pandrug-resistant isolates survived better in SW than susceptible or multidrug-resistant isolates. Two distinct colony phenotypes were recorded at extreme temperatures and pH values. The results of this study provide insight into the behaviour of this emerging pathogen in the environment.