​Kindly note that it is normal that exclusively breastfed babies may not pass stools for days or even up to 2 weeks and it is not something to worry about as long as the baby is well, not vomiting and not having swollen or hard tummy.
Do not give water or anything. Baby will definitely poo. Exclusively breastfed babies rarely gets constipated as breast milk is 80% water. Keep breastfeeding exclusively.