When we are dealing with a five day old, I think that if no other
supplement is available (expressed breastmilk), then full strength
artificial baby milk would be the appropriate supplement.  The baby
does not need more water than calories, fat or protein; the baby needs
everything.  Of course, the supplement should be given by lactation
aid, unless for some reason this is difficult.  But it is usually
fairly easy to use.

Jack Newman, MD, FRCPC