I do not know how many fasts have you done before. 20 days is a good goal, but if you can do following things you can go ahead and start.
1. Drink water as per thirst. Drink nothing but water, warm or room temperature
2. Rest plenty
3. No strenuous work and no stressful situations
4. Stay warm. Your body heals better when warm
I do not understand the last line, you are eating every 48 hours? If I understand you correctly you want to continue eating every 48 hours. I think you can eat every 48 hours but it would not be considered 20 day water only fast.