Water treatment at home isn’t difficult as long as it isn’t polluted with something bad like hydrocarbons. A distiller can be purchased for less than $100. There are many homes in Texas that are using heaters that aren’t heat pumps, so in the winter, it probably is economical if excluding the original purchase price. A reverse osmosis system can also be purchased for less than $500, but requires more maintenance.

> A brita-type filter will do precisely nothing for most things that require a boil notice

Well, it might do something, give a nice warm and humid substrate for bacterias to develop

What about the reverse osmosis filters many homes have?

I wouldn't say "many". RO is expensive and energy-intensive.

The under sink filters I'm aware of cost ~$200 and run passively off water pressure

Under sink filter != reverse-osmosis

Not all under sink filters are RO but some are. There are a variety of options on the market and the prices are much cheaper than bottled water over a year.

Right, but that doesn't mean all under sink filtration systems are RO. RO is a very specific method of filtration

We were talking specifically about RO filters. The one I have in my espresso setup cost a couple hundred and runs on water pressure, undercutting the claim that it’s expensive or energy intensive.

(They are water intensive - I would reconsider that if I still lived in California)

Not really. They aren't common in the US, but outside the US you can buy a $200 unit that will produce RO water a few gallons an hour.