In the recreation area Anička in Košice, there is a mineral spring that inhabitants call Gajdovka. It has been used with several breaks since the 19th century. Mineral water from this spring is specific by the presence of arsenic the concentration of which often exceeds the permitted limit level. This study focused on the analysis of the mineral composition of the spring water. Chemical and microbiological analysis was made in the years 2013—2015. In 2014, the mineral water Gajdovka was regularly monitored throughout the year with respect to the concentrations of arsenic, iron and hydrogen sulphide levels and water levels in the nearby river. The following mean concentrations were determined: total arsenic 0.063 mg.dm−3; iron 0.275 mg.dm−3; hydrogen sulfide 4.608 mg.dm−3. The concentration of iron was below the limit, while the limit for As(III) was exceeded in 2014 for 7 months. The statistical analysis showed that the season affects significantly the level of H2S and Fe and the water levels in the nearby river.