Water Rails (Rallus aquaticus) are a reliable indicator of overall habitat quality and are considered an umbrella species for reed bed habitat (Phragmites australis). Two methods of acoustic monitoring of Water Rails were tested. Ten observation points situated 100 m from each other inside a large reed bed were selected for acoustic monitoring. Observations were conducted in three sessions (end of April, June and September 2010) for three times a day, during 3 consecutive days. The number of individuals calling was quantified during spontaneous vocal activity for 5 min and then the number of Water Rails calling after exposure to digital playbacks of male and female territorial and courtship calls for 30 sec were recorded. To calibrate the data, all Water Rail nests within 100 m around three observation points were located. The number of nests found during the nest searches corresponded to the number of pairs estimated during spontaneous vocal activity, but was 63% larger than the number estimated after playback. A statistically significant difference was found between the number of calls recorded at different times in session 1; however, no significant differences were found between sessions 2 and 3. The highest numbers of individuals were recorded in the morning in session 1. The difference was statistically significant between morning and noon (P= 0.002), but not between morning and evening (P= 0.289). Population evaluation and monitoring of Water Rails in large reed beds should be done in the morning, during the breeding season, using point surveys and listening for 5 min for spontaneous vocalizations. This method can be used both for quantifying and monitoring populations of Water Rails and for evaluating the quality of its habitat.