I have a few questions.

I've read a lot about fasting on the internet. I guess my main question is do I have to do anything else besides just drink water? There are alot of things about colon cleansers ect., but I'm not to interested in that. Will I get results without using one of those? I also would rather not use laxatives, so what is best to take while on a water fast? I'm also going to continue exercising... that won't be harmful will it? Anyway, this is my first time, and I was wondering if any of you could provide some advise, it'd be very helpful.