Re: "dangers of giving breastfed babies water in hot weather", the best
reference I know is from a WHO Programme for Control of Diarrhoeal Diseases
Update, No. 9, August 1991, entitled "Breast-Feeding and the use of Water
and Teas".  It summarizes the six references done up to that date on the
use of water in breastfed babies and concludes that not only is water (or
other beverages) not needed but that the practice "is associated with
significantly increased risks of diarrhoea morbidity and mortality".  Hope
this helps your professor but at the same time I can't help but agree with
Dr. Newman that it is your professor who should be looking for references
to "prove" that breast fed babies need water, and not the other way around.
 I also have a problem with anyone agreeing that giving a child something
that is "unnecesasary" but not "harmful", is quite all right.  David.