I don't boil water, because I lazy.

Your concept is not wrong, just your assumption is a person drink boil water of 3 liter, but another person drink unboil water of 30 liter per day, which means both of them are drinking the same amount of mineral.

But I think their concept is, let's say a person drink 3 liter of water a day, and the person take 30 liter of water boil 50 times until left 3 liter, so basically he drank 30 liter water of mineral compare to a person drink 3 liter of non-boil water. So over the time, the person who drink re-boil water will have more mineral or some shit.