As an alternative to Water Fasting and the Master-Cleanse you could also take a look at juice fasting which is also great for losing weight. I have done both the Master-Cleanse and juice fasting and the results are similar in my opinion. If you change your eating habits after either the Master-Cleanse or a juice fast you will not gain the weight back. I started at 152 lbs and am now at 128 lbs. Most of the weight I lost doing the MC and a juice fast, then I changed my eating habits - I continued to lose some weight and now I seem to be steady at 128 lbs.
Go with your instinct. Listen to your body and it will tell you what it needs. Either way I would recommend going through previous posts to get a feel for the different fasts.