The objective of this study was to design a reliable questionnaire regarding hydration practice among athletes. Participants were students recruited from the University of Split, Croatia. The questionnaire consists of 28 questions; gender, age, body mass and height, health status, years of training, weekly and daily length of training, intensity of training, hydration habits during training, etc. The same participants conducted the questioning twice, one month apart. In the eligibility and validation of each question, the Pearson correlation coefficient assessed the reproducibility of the quantitative data, while the corrected Cohen’s d assessed the reproducibility of the qualitative data. Chi-square tested hypothesis (H0=The data follow a specified distribution; in this study – no significant differences in the average answers (after one month) were established). The values for Pearson correlation coefficients should be as close as possible to 1 and the values for corrected Cohen’s d should be as close as possible to zero. Pearson correlation coefficients ranged from 0.0625 (e. g. for amount of liquid amino acid intake) to 1 (e.g. for frequency of liquid amino acid intake prior to training). Reproducibility was accepted and chi-square confirmed our hypothesis.