Quick take
Carbon filtration is enough when taste is the only concern. In very hard-water areas, RO or softened/remineralized drinking water can sharply reduce kettle scale.
Why kettles scale
Heating hard water concentrates calcium carbonate deposits on the element and vessel walls.
Carbon helps taste, not hardness
Activated carbon can improve chlorine taste but does not meaningfully remove the calcium and magnesium that drive scale.
RO reduces scale
RO removes much of the dissolved mineral load, which can greatly reduce kettle deposits.
Balance taste and maintenance
Very low-mineral water may taste different, so some households prefer remineralized RO for drinking and hot beverages.