Makes some sense, still, especially for renters, if they don't want to have to move the system and have a big (yes, it's big to some people) up-front expense. I

Makes some sense, still, especially for renters, if they don't want to have to move the system and have a big (yes, it's big to some people) up-front expense. If it's just for drinking water, it looks like you can get over 2500 person-days of drinking water in the form of CostCo 16.9oz 40-bottle packs ($2.95 for 40 bottles) for the same price as a cheapish RO system (~$200—you can buy about 333.3 gallons of that Costco water for that). About half a liter of plain water intake per person per day on average, in the US, from what I can tell. Even if you double that to account for tea and coffee, that's about two years' drinking water for a couple. Considerations: that's not even the cheapest filtered water one can buy, and the RO system has consumable filters (= more expense—frankly, I wouldn't be surprised if the bottled water is straight-up cheaper, overall), maintenance, and installation to worry about. I don't think buying bottled water regularly is necessarily irrational. FWIW, we do have an under-sink filter on our kitchen sink rather than buying bottled water, though I'm not convinced it's justifiable based on cost—we don't live in so-bad-you-can-smell-the-water land anymore, but the filtered stuff still tastes a lot better, and it's nice not to have to remember to stock up on water at the store, though we're so bad about maintaining the filter that I think if we did it right the extra time and more-stuff-to-remember would make buying drinking water more convenient after all)