Water for dehydration

Hi everyone

So my daughter (just over a month) has always been quite sporadic with her poos - she's exclusively breastfed and obviously that's quite normal. However, the health visitor told me that if she goes over a week without anything (she wees a LOT and is putting on weight so it's more of a congestion issue) to call the doctor. I'm calling in the morning for an emergency appointment, but in the meantime I'm wondering if anyone else had heard of giving baby a tablespoon of clean, boiled water to aid things along?
Thanks in advance.