Hi,
Not too much a difference between regular water and flavored water.... What bothers me is that you think "it is not such a good thing".... my friend, it is a VERY BAD THING !!!!! you make an irreversable damage to your body.... You'll have to force yourself drinking (if you don't remember use an alarm clock to remind you....). it's not a question weather you like it or not it's a MUST !!!! (specially as being a teniss teacher, lossing rivers of water). By the way, you should teach it to your students (to drink regularly during the game).
Best regards,