Fluid and electrolyte imbalances can compromise physical performance of professional athletes. We have conducted a study to understand how aware athletes are of their hydration status and how they deal with dehydration. First, we surveyed 51 athletes (mean age of 20.4 years) specializing in different sports, including ice hockey, water polo, tennis and figure skating, using a questionnaire. Next, we analyzed the anonymized results of the laboratory tests run on the samples of 30 athletes specializing in futsal. We focused on hemotocrit and sodium levels and urine specific gravity as indirect indicators of hydration status. Survey results demonstrated that 86 % of the participants lacked knowledge of wise approaches to replenishing fluid or electrolytes after physical exercise, did not adequately control fluid intake and developed various degrees of dehydration. We noticed that awareness of hydration status negatively correlated with professional qualifications of the participants. Retrospective analysis of laboratory tests showed that hypohydration prevailed among high-class athletes: at least 73 % of them showed signs of dehydration. We emphasize the need for elaborating unified clinical recommendations on rehydration for Russian athletes that should be further approved by doctors and coaches.