Softener and carbon in one tank
A softener and a carbon filter are usually sold as two separate tanks. A mixed bed puts both stages in one, so the system takes less floor and has one control head instead of two.
Hard water goes through the softening stage, then the carbon stage takes the chlorine taste and smell out before the water heads to the rest of the house.
Sized to your household
Tank size comes from how many people live in the house and how much water they use. Too small and it runs out between rinses, too big and you pay for capacity you never use.
That is what the short assessment call settles, before any number is written down.
Where it goes in the house
A whole home system goes where the main line comes in, which is most often a basement, a utility room or a garage.
It needs a drain for its rinse cycle and an outlet for the control head, and enough room to open the salt cabinet.
City water, chlorine and hardness
City water arrives treated, and the chlorine used to treat it rides along to every tap. Hardness was never the utility's job, so it arrives too.
One system handles both where the water enters the house. Drinking water gets reverse osmosis on top.