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)