To know how much extra water you should drink, you should weight yourself before and after your workout. For every pound lost during exercising you should drink 500 ml of fluid. You should also drink water before (250 to 500ml 1 hour before exercise), during and after working out.

Remember to keep yourself hydrated throughout
the day. In case you have any alcohol or drinks with caffeine (hopefully you
will avoid them), try to drink at least one glass of water for every drink you
have.