Originally Posted by Unibrow
But I finally isolated the 1 variable that elevated home brew from good to outstanding: using only store-bought spring/distilled water
I would respectfully amend your statement to say: Don't just assume your water is good. Understand brewing water chemistry enough to provide good water for your brew!
That may mean you can use your tap water, or buy water, or get an RO filtering setup, or whatever.
But don't just blow it off, or buy the "if your water tastes good it's good for brewing" advice. That's a recipe for possible disappointment and waste of good money and time. I made that mistake and ended up brewing way too much beer that just wasn't good due to astringency, aftertaste, etc. My water is chock full of minerals, but really isn't bad for drinking water, IMO.
So pay attention to your water first!