Kids are like that. No matter how you ask them to drink water they will reject. It takes time, slowly and surely. My firstborn has difficulty drinking water. So we bought her sippy cups and put little water for her to drink. Going to school we ensure and encourage her to drink water. Even if it is minimal, atleast hydrate a little rather than not drinking any water at all besides FM. We also encourage her to have fresh milk or juices in her sippy cup. And also ensure no sweet drinks like Pokka Tea, etc for her. Hope this helps. But dont worry much as long as your LO drink a little. Sooner or later, they will get use to it.