Urinary tract infection (UT1) is influenced by daily fluid intake, and there is a positive correlation between UTI and slowing down of urinary flow within the urinary tract. In this study, the dynamic of fluid intake and output during school hours among Turkish primary school children was analysed, and the relation of this dynamic to UTI in accordance with the impact of socioeconomical status of these children on this relation was evaluated. The study was carried out in 17 primary schools, and 1024 children (516 male) were enrolled. A questionnaire related to daily fluid intake and output in school, and daily activities that could effect this fluid dynamic was completed by each student. After that, a clean voided midstream urine specimen was obtained from each child, and evaluated by dipstick and light microscope. Pyuria, bacteriuria and pyuria + bacteriuria were determined in 20.6, 7.8 and 6.2 percents of the children, respectively. When the children were analysed with respect to the mean water intake during school hours, "those drinking water in every two breaks or more frequently" and "those drinking water every three breaks or less frequently or not at all" were 491 (47.2%) and 533 (52.1%) respectively. Decreased water intake during school hours was associated with an increase in the rate of pyuria (p < 0.05). There was a negative correlation between the frequency of urination (FU) in school and the developmental status of the areas in which the schools were found (r: - 0.117, p < 0.05). A significant relation was found between pyuria and FU in school (p < 0.05). The rate of pyuria was 15.2 and 22.2 percent in "those urinating in every two breaks or more frequently" and "those urinating every three breaks or less frequently or not at all", respectively. There was not a significant relation between FU in school and neither bacteriuria nor pyuria + bacteriuria (p>0.05).