We've personally only had experience locally with the Culligan/Primo stations (Primo technically bought out Culligan's vending machine division a couple years back) and whatever filtration system Whole Foods uses, which includes a full DI filtration option at our local store.
At home, Zerowater seemed like a promising solution for us initially for the price, especially through double filtration, but I'd calculated filter longevity on dated information from our own water utility expecting chlorine instead of chloramines ourselves. We got about ten gallons on the first filter before it blew out, expensive mistake... but the water was tasty while it lasted. *chukle*
If you're getting serious about water quality, it might be worth the ten bucks or so to pick up a
TDS meter. It won't tell you
what contaminates are in your water, but it'll give you a quick idea of how much total contaminates are there. It'd probably be useful to determine who has the best filtration system locally. Of course, going filtered DI or under 10ppm (technically anything under about 50ppm, IIRC) primary water drinking starts getting into other issues like stripping out trace minerals and salts in the body, though that's easily countered with regularly using stuff like Himalayan salt in all your cooking. If you keep solid particulates under about 5-10ppm though, you can pretty much guarantee that it's practically fluoride and chloramine free, not to mention very soft water, which mostly gives you a mostly blank slate to treat and tinker with if/as needed.
I can't remember exactly what precipitates back out long term on the ascorbic acid front and I'm feeling lazy trying to call it back up, but as Axial Gentleman pointed out, the long-term end product was still deadly for his betta... it's more useful as a neutralizing agent pre-filtration. Regarding UV treatment, it is something that still should have post-filtration, but again the key is to neutralize the chloramines to prolong GAC longevity and sterilization. A good starting point on the science
was mostly pioneered in pool care, but has since extended into water treatment for breweries, hospitals and larger scale bottling operations as well. A key search term for chlorimine mitigation technologies interestingly enough is kidney dialysis. I'm personally still researching the UV front myself, but can't seem to find any units under $2500 that doesn't also handle something like 50+GPM, which is ridiculously overkilled for any size family. If I find anything before you do, I'll share.
Your water utility is technically right on the stability of the chloramines, it is considerably more stable long term which is why it's so difficult to remove, but the effectiveness for killing microbes is nowhere near as effective. As for greater chloramine research in general, the
CCAC out of San Francisco has a good website to start to fall down the rabbit hole on with the stuff.