You may want to peek on the Master Cleanse Forum - it is almost like what you describe and people have done this cleanse for 40 days safely - if you go beyond that, it is up to you to listen to your body but I believe you will need the nutrients of food to be very healthy. The theory of cleansing is generally periods like this to cleanse, then periods of eating healthy to rebuild your body's strength, then back to cleansing if more is needed. A cleansing diet that is full of nutrients but very stripped down/healthy/basic is the Raw Foods Diet, if you are concerned about weight/health/nutrition.