Health visitors

No`5 🐝 happy • Religion - Jedi. Cares about - my children. Things I find funny - actual religion. Dislikes - fancy foods.
I have three children my eldest is 16, with my first I listened to health visitors which lead to a very unhappy baby, I was told no water was to be given, the kid ended up with mild dehydration, don't do this don't do that! Well by the time I had my second I sack her off altogether and refused entry and had a very happy baby, she had water when she was thirsty even from birth, her bottles were warmed up and pre-made and chilled! I did the same the things with both of my other two children and happy healthy weight gaining babies!
However my SO's sister had a baby two months ago, and this woman listens to the health visitors like her word is gospel! Can I add this woman has NO kids! This baby is thirsty all the time and just not a happy kid at all! She is given cold milk, and she hates it! But the mum refuses to back down on anything unless the health visitor says so.
I offered to feed the baby while she did some house work and this kid was screaming hungry, so I heated up her bottle and she ate like she never ate before, I got a almighty telling off for heating the bottle up. On that note I told her you have been a mum 5 mins I've been one to 3 kids 16 years I think I know what I am doing and if she didn't listen to a text book and statistics so much she would have a happy baby! 
Even her mum has suggested other ways to Pacifie this baby, but nope, unless it's written in a text book she won't have any of it.  I know there will be women on here that swear by the text book, but for personal Bally my babies are not in a text book not are they a statistic.  I listen to what the child needs not what the book says.
What's everybody's thoughts on this