My First Water Fast - A few questions

I'm 20 years old and currently weigh just under 280 pounds, and just finished 1 day of my post-thanksgiving water fast, and I'm not even very hungry!

I'm doing this fast for weight loss, but more importantly as a jump-start to healthy eating, detoxification, and as an exercise in self-control.

My eating habits were very bad before this, and I've read that Water Fasting can be dangerous if your body is "polluted".

Originally I planned on doing a 30 day fast, but now all this stuff I'm reading is starting to worry me.

My plan was to go at least 7 days, see how I feel, and go from there. I would like t o eventually transition into a more long-term juice fast, once I can prove to myself that I have the self-control, and can justify buying the juicer :P.

My question is how long can I safely do this? What are warning signs that a fast is becoming unhealthy?

Any helpful hints for a newbie water faster would be much appreciated.