As someone said, you can leave and be led out by the proctors but you will get less time to finish your exam (remember the average time is if I’m not mistaken 1.5 minutes per question if it hasn’t changed lately). If you finish after around 2.5 hours you may leave then, but during the final half hour nobody is allowed to leave. Plan accordingly… Someone will follow you to the loo I think, and stand right outside the door, and you can’t access handbags or anything like that.
in toronto for example, the exams are in big exhibition halls which have toilets inside a room built into the back of the exam room, so you don’t leave the exam room, and a proctor is paid to sit in the corridor by the stalls
Due to the possibility of spills, that may cause damage to exam books and candidates’ exam sheets, candidates are not permitted to have water bottles next to them. However, water stations are provided in the testing rooms at convention halls and drinking fountains are accessible at universities and schools where the CFA Exam takes place