Sick of students asking to go to the bathroom, get a drink, tell you how dry their throat is? Solve that problem by giving them a limited number of "tickets" out of class! I photocopy them on bright paper and give each student a sheet of tickets. It is up to you how often you want to re-fill their tickets. (One sheet per term, etc)
Students are not allowed to go anywhere without a ticket! Then, keep their tickets upon their return as the restroom log.