I am sorry, I don't know.
I don't see why saving the water would hurt. If nothing else, it will make yummy infant cereal later. If your LO has constipation problems, pear juice and pears cut up into small pieces work as well as prunes/ prune juice. but are more gentle on the tummy.
My DS1 was backed up from 4 months until 2/5 years. I still make sure I have pear j. on hand.