I don't even like to see recommendations for IPA (isopropyl alcohol). In 95%+ of the cases ethanol (ethyl alcohol) is just as good and is way less toxic than IPA.
The stupid problem is that it's taxed heavily and thus is stupidly expensive. When not taxed it is probably denatured, but denatured with what? If you know the denaturant then you can use it with some degree of confidence. Methanol (methylated spirits) is acceptable in almost any technical application but is somewhat toxic, so for stupid reasons it is now rare. Denatonium benzoate is the other common denaturant, but it can leave annoying residues behind. Pick your poison (literally).
At one point in my career we had ready access to untaxed, undenatured, 200-proof absolute ethanol. So I used it a lot! Turns out it's significantly more aggressive than isopropanol, and can strip coatings or generally even dissolve things that isopropanol cannot. I don't use ethanol any more, I have better things to do with my life than figure out what it is and isn't going to dissolve.
I haven't heard that IPA is much worse than ethanol though, beyond what's stated on Wikipedia ("somewhat more toxic"; ethanol is obviously toxic as well). Should I be more concerned about using IPA?
Not really. The entire planet was rubbing it on their hands for years during the pandemic. It'll dry your skin out, sure, if you're getting a lot of it on your skin, but you shouldn't be if you're not using it as hand sanitiser, and of course you're not drinking it.
The white residue is a separate problem. Alcohols are not perfectly effective at dissolving all the components of flux residue, so you often get white crud left over. It's harmless, but ugly, and sometimes you just need a clean joint. I think it is possible to get this stuff off with alcohol and some skill, but who has time for that? Just buy proper flux remover.
The best flux remover I know of is MicroCare SuprClean or PowerClean (they're very closely related, but definitely at least a little different; either way it's hard to tell them apart, so go for whatever's convenient). It is supposedly nontoxic (but remember they once said that about the last flux remover that got banned... and the one before that... and...), readily available from the usual places here in the US, and very, very powerful. Careful cleaning with it will not leave any white residue behind. (Careless cleaning will lead to the observation that flux remover solvents dissolve soils... which means the soils are right there to be redeposited should the solvents evaporate... so you have to actually manage to get the crud off the board if you want it clean. Dissolving alone is not enough!)
I haven't done an exhaustive survey of flux removers, but this stuff certainly does the trick. I was originally looking for something that could dissolve Krytox residues (long story) and while I thankfully never had cause to test it, this stuff is based off some member of the Vertrel family, which is one of the few things in chemistry capable of that job. And anything that can even threaten Krytox is probably a tool worth having!
Nearly any properly designed board will not hold residual voltage for long when disconnected from power, so the slight conductivity of tap water is a non-issue.
(Much discourse on industrial safety casts corporations as the bad guys, with considerable evidence, but it is still the case that much safety equipment is bulky or unpleasant to use. Ketone-proof gloves are thicker and less pliable than latex gloves, which is no small consideration when doing fine work under time pressure. Easier to just wear two layers and change the outer glove when it starts to break down. When do you know it's breaking down? When you feel it leaking through. When you feel that, doesn't it mean you're already getting skin contact with the solvent. Well, yes, but....)
As far as I know, there has never been a fatality attributable to MEK exposure. https://en.wikipedia.org/wiki/Methyl_ethyl_ketone#Health_eff...
You can get Isopronaol on Amazon.
B: Isopropanol isn't that toxic. Much less so than methanol, for example.
It's still tricky most places in the US -- you will likely have to jump through hoops to pay taxes and/or get the license to purchase, depending on your state's rules. I agree that IPA is not enough of a concern to actually justify it in my mind.
Even worse, I've seen people recommend h2o. You can drown in that shit.