A total of 145 schoolchildren in Year 2 (aged 6-7 years) and 153 in Year 5 (aged 9-10 years) classes were studied in six Southampton schools. Total fluid intake and toilet visits were recorded during one school day. Schools were recruited according to drinking policy: 'prohibited access' = water prohibited in classroom; 'limited access' = water allowed in classroom but not on the desk; and 'free access' = water bottle encouraged on the desk. Data were analysed on an intention-to-treat basis.