Put your hands under warm running water and gently rub them together for 15 minutes immediately after they are exposed to the blue toilet water, according to 2000 Flushes, a major manufacturer of blue automatic toilet bowl cleaners.
Wash your hands with white vinegar to help remove any blue stains left behind after washing them under water. You can also use rubbing alcohol to help remove the blue from your hands.
Wash your hands using a mildly abrasive hand cleaner, such as one with pumice in it, to remove any remaining blue stains. Alternatively, combine baking soda and water to make an abrasive cleaning paste. Rub your hands together with the hand cleaner or baking soda mixture to exfoliate the skin, which will help take off the blue dye.