It is a 7 year old message, but people still read for information. For centuries, waterfasting during pregnancy has been considered safe as long as the mother is not a diabetic, as diabetic ketoacidosis is very dangerous for baby and mother.
Ketosis (the state generally obtained through water fasting) can actually be beneficial for both mother and baby during pregnancy.
During breastfeeding, waterfasting can be quite dangerous as it exposes the baby to dangerous levels of toxins in the milk.