Exclusively breastfed, low birthweight term infants do not need supplemental water.Acta Paediatr. 2000 May; 89(5):550-2.AP
Breast milk intake, urine volume and urine-specific gravity (USG) of exclusively breastfed, low birthweight (LBW) term male infants in Honduras were measured during 8-h periods at 2 (n = 59) and 8 (n = 68) wk of age. Ambient temperature was 22-36 degrees C and relative humidity was 37-86%. Maximum USG ranged from 1.001 to 1.012, all within normal limits.
We conclude that supplemental water is not required for exclusively breastfed, LBW term infants, even in hot conditions.