My letters play tricks on sight, R or A? A or R? Shuffle me and you will find, I am my own definition. What am I?

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

I'm a concept that most would say is the natural course of a person with empathy, My name sounds like it could be the ideology of people that never speak a lie, but that's not exactly my followers' tendency, To help and promote others, while expecting no personal gain, I'm a great trait for a person, even if my prevalence has been tending to wane

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.

The kind from Brussels are not the most favourite on the planet, although some say that roasted they're not half bad.