Sounds like you are being very sensible about increasing slowly.
Not everyone believes Water Fasting is even 'good for you', and if you yourself have any ideas, or just a 'gut feeling' in your own being (even old, suppressed belief systems of others), that it might be 'hard on you', these will tend to prove the thesis, if you will.
But as they say, everyone is unique, and even within one life, we are unique to 'the season'. You know, like the song, "to everything, turn, turn, turn... " What feels impossible one year, or one month, is perfect the next. As long as I feel in any way sensitive to the changes I am taking on as challenges, I find it really useful to go with the moon cycles. To try to begin a project like fasting near the new moon, or at the very least, prior to full moon. This seems to help a LOT. It's like having inner support for what i say I want to do.
if I were "re-mineralzing" also, I'd want to build it up, as the moon waxes. But maybe you're someone who has a strong venus, . . .
For me, the moon is quite prominent in my natal chart. Almost like the sun at high noon.