Legionella pneumophila is a gram negative bacterium found in different natural water environments, as well as in artificial water systems. Inhalation of aerosol infected with Legionella develops in a man a Pontiac fever or a severe Legionaires disease. With the growing awareness of legionellosis associated with usage of pools and jacuzzi, regular cleaning and disinfection become a key risk factor for spreading infection. In addition to heat and chlorine disinfection, alternative antibacterial agents such as essential oils extracted from various plants are increasingly evaluated. Therefore, the aim of this study is to determine the synergistic anti-Legionella effect between selected essential oils and the synergistic effect of essential oils in preventing biofilm formation in order to establish an alternative water disinfection method. Essential oil of lavender, rosemary and immortelle was used, and the examination was carried out using the chessboard method with the usage of microtiter plates. The obtained results show the synergistic and additive affect of these essential oils. The minimum inhibitory concentration of rosemary essential oil is 12.8 mg/mL, while the minimum inhibitory concentration of lavender and immortelle essential oils is 3.2 mg/mL. When essential oils produced a synergistic effect, much lower concentrations (0.05 to 0.8 mg/mL) were needed to suppress Legionella than when only one essential oil was in used. These essential oils have also shown a synergistic effect in preventing biofilm formation. In conclusion, the best anti - Legionella effect was shown by a combination of lavender and rosemary essential oil.