This riddle is really short, I hope you don't mind. Whst does a house wear?

I'm a most dangerous substance, responsible for over thirty deaths every hour, Hydric Acid, Dihydrogen Monoxide, my many names demonstrate my great and varied power, Used in Nuclear reactors and even as a great fire suppressor, You actually have me in your body, but don't for that think of my hazards as any lesser

High above the world, I stand, a stage for skies to meet the land. A ledge where whispers softly blend, where views and breezes gently mend.

PROOF TO rain and wind and sky, Rearrange me, that’s the why. Split in two, both halves are true, The answer hides in plain view.

I reflect the heavens down below, born when storm clouds overflow. Step too near and watch me sway, as ripples steal the sky away.