Um..I wouldn't suggest Water Fasting for a first fast. It's way too hard for a first fast and it can be dangerous with the more toxic you are. Instead of concentrating on just the weight loss, your main goal should also be health, detox and cleansing reasons.
You won't keep the weight off with any diet if you go back to your old way of eating. The reason people always gain weight after Atkins is because they still don't understand how to eat. They do the diet, and then go off it and go on a high carb/crap food craze. Even if you do lose 30 or 40lbs fasting, if you go back to whatever made you gain weight in the first place.. it will happen after the fast too.
"on and off the WOE'.. let me guess, cravings and boredom?
Most of the weight you gained is probably water and crap too..Most people get really backed up on Atkins even if they're still "going" during the day.
I'd suggest The Master Cleanse for a first fast. It's easier and if you like the taste of the lemonade it'll be even easier to stick with it. (The main thing with that is finding a decent brand of maple syrup..some are nasty) You have to be mentally prepared for it though, so you might want to read over in that forum for at least a few days so you know what to expect. The first couple of days on any fast are the hardest with detox headaches and if you don't know what to expect, you'll fail and "yoyo" again. Go to http://www.themastercleanse.com and read up on that one.