I agree, water isn't necessary yet. When I was out and about the other day my baby had hiccups and a lady started saying to her in baby talk "Oh, mommy's gotta get you some water" over and over and I just smiled and nodded, haha. I just agree with what random people say, but know that I won't do it if I feel like it's not in my baby's best interest. If my parents give suggestions I don't agree with I tell them the way I want to do things and ask them to respect my choices, so far they have.
As far as the pediatrician goes, I've learned to take everything they say with a grain of salt. My baby's doctor told me to put a little cereal in her bottle to help her sleep at night when she was 1 week old! Then proceeded to tell me that sometimes it can cause constipation so it would be okay to give her a little bit of Gerber juice. I was under the impression that doctors do NOT recommend cereal in a bottle except for some situations like reflux, so when she said to put cereal in my 1 week old baby's bottle I had to pick my jaw up off the floor! The juice suggestion was just icing on the cake.