Reverse osmosis is excellent at removing contaminants — but the same fine membrane that blocks sediment and heavy metals doesn't distinguish between what's harmful and what's beneficial.
Calcium, magnesium, and potassium are all small enough to pass through most RO membranes, meaning naturally occurring minerals are filtered out along with everything else.
Alkaline systems typically add a remineralization stage after filtration, reintroducing a controlled mineral profile so the water isn't left completely "empty."
The practical difference shows up mostly in mouthfeel and pH stability: remineralized alkaline water tends to hold a steadier pH over time compared to straight RO output.
Neither approach is right or wrong on its own — they're simply solving for different priorities, and the remineralization step is what separates the two in practice.