Hey dear dont give water to 4months baby .as it s not safe to give water to baby before 6months ..if baby s taking breast milk water s gling through breast milk nd if baby s taking formula milk then also water goes wit milk as v make formuka milk in water too..so in both suitation water s gping through milk..there s no need to give additional water to baby ..give only breast milk untill baby completed 6months . take care