That decision comes years or decades after practice and learning, which people do because A) they find just noodling on the instrument fun, and/or b) they find improving their skill deeply rewarding, and/or c) they think guitar/music is just really cool.
A bad instrument can make the experience miserable, though. My first acoustic was fucking awful, just straight trash. How long does yours stay in tune?
I work at a plant that uses one of those alternative flocculants (due to our source water chemistry). Our logistics are incredibly shaky at the best of times, due to the extremely limited number of producers.
Most bottled water comes from a municipal water system somewhere, i.e., is tap water.
Some water supplies have issues with sulfur or algae, so that can be unpleasant if your sense of smell is particularly sensitive. My sense of smell is pretty weak so I drink the tap water most places, while my spouse had an RO system installed in our house due to their sensitivity.
Supplements suck that way, sorry. I've found a couple brands that work for me (Nature's Way, Horbäach), but I'm no supplement expert. I'd try to find a mid-price option that didn't seem too sketchy.
As for nootropic stacks and whatnot: never heard of them, although they seem interesting. I personally take 2g of tyrosine along with vitamin D and a vitamin B complex (plus a couple medical rx). I would start at 500mg-1g, and add more after a week if you felt you needed to. I have taken tyrosine with omega 3s but never regularly; I didn't notice an interaction at the time.
Tyrosine. It's a dopamine precursor. By itself, it mildly increases focus just enough to get non-preferred tasks started. It also makes completing tasks much more rewarding, which can start a positive feedback loop that leaves your space much more livable/less depressing.
Learn yer (smith &) wesson