Water is two parts hydrogen and one part oxygen. What if...

Water is two parts hydrogen and one part oxygen. What if someone says, “Well, that’s not how I choose to think about water.”? All we can do is appeal to scientific values. And if he doesn’t share those values, the conversation is over. If someone doesn’t value evidence, what evidence are you going to provide to prove they should value it? If someone doesn’t value logic, what logical argument could you provide to show the importance of logic?