Carbon Filter and Water Softener: Do You Need Both? (Complete Guide)

A carbon filter removes chlorine, chemicals, and taste issues. A water softener removes hardness minerals. They solve completely different problems, so the real question is which problems your water has. If you're on city water and it's hard, you need both, and the carbon tank goes first so the chlorine never reaches the softener. If your city water is soft, or you're on a well with no chlorine, taste or smell, one of the two may be all you need.

A caller near San Diego on city water had just been told the resin in his softener was finished: "This thing worked for about 11 years. They said the resin's gone." The replacement he was quoted was $6,750. The first thing I told him is what I tell city callers: "First, you wanna put a carbon tank in first to take the chlorine out, because the chlorine shortens the life of the resin."

What each tank takes out

A softener traps the calcium and magnesium in your water and trades them for sodium. A carbon tank grabs chlorine and other chemicals as the water passes through it. Neither system can do the other's job. As I tell callers, "The softeners don't remove chlorine, they only remove hard water," and carbon leaves the hardness in.

For the longer version of how the two machines work, see the difference between a water filter and a water softener, or watch the short video below.

Which setup your water needs

On city water, you need both when the hardness is 7 grains per gallon or more. Below 7, I tell people it's not an issue; the Minnesota Department of Health puts its line in the same place and says plainly, "There is no requirement to soften your water." Find your row:

Two calls show both ends of it. A condo owner on city water had been quoted over $8,000 for a softener system by an in-home dealer. Her hardness was 5.6, so I told her she didn't need a softener at all. Anything below 7 grains is fine, and a carbon tank plus an under-sink reverse osmosis unit for drinking water was all she needed.

The other end was a well with 15.7 ppm of iron, where a national dealer had put in a softener and a carbon tank. "It's not really doing the trick," the owner told me. That much iron needs its own iron filter ahead of the softener; a carbon tank was the wrong filter for that water.

Not sure which row you're in?

Text Aidan your hardness number

City water: your hardness and how many people live there. Well water: your lab report. He'll text back which tanks you need, or tell you if one is enough.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

Which tank goes first?

On city water, the carbon tank goes first and the softener second, so the chlorine is gone before the water reaches the softener. It's how my own house is set up: I'm on city water, with a large carbon tank and then a softener. On a well with no chlorine, the order flips and the carbon tank goes last.

City water, first to last:

1. Carbon tank
2. Softener

Well water, first to last:

1. Sediment filter (5 micron), right after the well tank
2. Acid neutralizer or iron filter, if your test shows low pH or iron
3. Softener
4. Carbon tank (a UV light, if you have one, goes after it)

How chlorine wears out softener resin

Chlorine is in city water to kill germs, and it attacks the softener's resin beads too. Purolite, which makes softening resin, puts numbers on it. At about 0.3 ppm of free chlorine in cold water, the resin loses little of its life. As a general guideline, though, each 1 ppm of chlorine in the water cuts the life of a premium softening resin in half, and each ppm after that halves it again. The higher the resin's crosslink, the better it holds up.

Every softener we sell uses 10% crosslink resin, the tougher grade. Kept away from chlorine and iron, it has lasted 30 to 40 years in my service work. On city water, the carbon tank is what keeps the chlorine away from it.

Carbon goes last on a well

On a well with no chlorine in the water, there's nothing for the carbon to protect the resin from, so its job is to polish the water at the end: it takes out taste and odor and reduces herbicides and pesticides. The things that do hurt resin on a well go ahead of the softener. Iron shortens the life of the resin and sediment can clog it, which is why the iron filter and the sediment filter come first.

An acid neutralizer goes ahead of the softener too. The calcite in it adds about 3 to 6 grains of hardness as it raises the pH, and the softener takes that out. Which of those two goes first depends on your test; text me the report and I'll tell you. For every stage in order, see the correct order for well water treatment.

Which package fits your house

For city water we sell two carbon and softener pairs: a smaller one for 1 to 4 people and a bigger one for 5 or 6. Both carbon tanks are the non-backwashing kind, with no drain and no power.

For a family, I lean toward the bigger softener: "the less it regenerates, the less salt you're gonna go through." Over about 30 grains, or 7 or more people, text me and I'll size it.

In this video I answer the questions people ask me before they buy the pair: whether you need both, when the carbon tank alone is enough, which package fits your house, and one tank or two. The softener on the bench is a 48,000 grain; the bigger package pairs the 2.5 carbon tank with the 64,000 grain.

Packages for well water

On a well, your test picks the softener's partner.

What comes in the boxes

Both tanks ship empty, with the carbon and resin packed separately to pour in at install. A full tank is too heavy to ship.

• The carbon tank: a Clack non-backwashing head (upflow: the water runs up through the carbon) with a bypass valve, on an empty Vortech tank, plus the Centaur carbon in boxes: 1.5 cubic feet in two boxes with the small package, 2.5 cubic feet in three boxes with the large one. A fill funnel comes with it.
• The softener: the Fleck 5600SXT valve with its bypass valve already on it, an empty Vortech tank, the salt tank, and the 10% crosslink resin in bags (1.5 cubic feet with the 48,000 grain, 2.0 with the 64,000).
• Not in the boxes: the 1/2 inch drain tubing for the softener (any hardware store), the pipe, fittings and adapters, and the salt.

The makers put little or no install guidance in the box, so use how to install a water softener, and call or text me with questions. The two tanks can arrive in more than one shipment. Shipping is free to the lower 48.

Who installs the two tanks

I recommend having a plumber put it in, and I'm a phone call away for your plumber. Two tanks in a set order is a bigger job than one, and it's where a plumber matters most; one who has put in water treatment before is ideal.

The carbon tank is only an inlet and an outlet, with no drain and no power. The softener adds a 1/2 inch drain line with an air gap to a floor drain, standpipe or utility sink, an outlet for the valve, the brine line to the salt tank, and its settings. On city water the carbon tank goes in first. Plan on about 3 to 4 hours and about $700 to $1,000 for a plumber to put in both. If you'd rather do it yourself, text me at 443-277-2204 with any questions.

What it costs to run both

Running both comes down to salt for the softener and new carbon about every 5 years. There's no cartridge to change.

Changing the carbon is the head off, the old carbon out into trash bags, and new carbon poured in with the funnel. The tank stays.

Frequently asked questions