My girl doesn't like drink much water either. Not sure if your bb uses milk bottle or cup to drink water. Some bb doesn't like to drink water from the milk bottle as they consider milk bottle is for milk and not for anything else. My girl is one of them. When she was 2 months old, she refused to drink water from the bottle and I used a spoon to feed her. I have been using cup to feed her since she was 6 months old.
Recently I gave her a new cup with a straw and she drinks much more. Most bb like new things and like to drink like an adult. You may try this and see if the situation improves.