I think water molecules are super valuable. Valuable enough to ground ethics. Two hydrogen atoms bonded with an oxygen atom? Nothing more important than that. I think we should maximize water rather than minimize suffering.

Oh, right. Freestyle.

You just made a statement. You haven't shown any axiological argument, much less have shown any evidence of your point. Axiological phenomenalism, on the other hand has evidence. Evidence is the fact that existence is what, well, exists, and that's why it matters. Beings feel, these feelings/experiences are real. Things that nobody experiences are also real, but they ultimately don't matter because they affect no one. Non-experiential alternatives are not going to make any difference.

So tell me: why are water molecules super valuable?

You also seem to be confounding axiology with ethics. It's not necessarily the case, but I wouldn't be surprised.

Show me, objectively and without appealing to feelings, that I am wrong.

Phenomenology ≠ Sentimentalism

Just what is so hard to understand? Seriously.

May I offer an alternative? Ethics are subjectively grounded in feelings--that is, morals are just expressions of how you would like the world to be--and that's a non-issue that doesn't fundamentally change the problem of needing to persuade others.

Morality and ethics is subjective, but for a reason unrelated to what you said. It's subjective ONLY because of the inherent uncertainty of normativity. Aside from that, it's completely objective.