Background Ageing is inevitably associated with a progressive cognitive decline. With the rising percentage of the elderly in society, the number of people with dementia and cognitive impairment increases. Water is a vital ingredient that must be included in the diet. The impact of hydration status on cognitive performance has been studied only a little so far. Aims The objective of the study was to investigate the relation between the hydration status and the cognitive function. Methods The study was conducted among 60 free-living volunteers, aged 60–93 years. Data on water consumption were gathered based on 3-day records. The hydration status was assessed in morning urine samples by evaluating urine specific gravity. The cognitive function was tested using the Mini Mental State Examination (MMSE), the Babcock Story Recall Test and the Trail Making Test. Information about depression was gathered by the Geriatric Depression Scale. Results The mean daily total water intake was 2441 ± 622 ml, and 70% of respondents met the reference values for an adequate intake. The mean urine specific gravity (1.013 g/cm 3 , range of 1.004–1.025 g/cm 3 ) indicated that most of the individuals were in a good hydration state. The average result of MMSE was 27.8, which is connected with mild cognitive impairment. There was no significant relationship between the hydration status and the results of the cognitive function test in the studied population. Discussion/conclusion As the elderly volunteers had a good hydration status, there was no significant relationship between cognitive performance and urine specific gravity. It is necessary to replicate the findings of this study with a larger and more diverse sample of older adults.