Can I Pair a Water Softener With a Whole-House Carbon Filter?

Written by Craig "The Water Guy" Phillips

Yes, a water softener and a whole-house carbon filter work well together, and on chlorinated city water the carbon filter should go before the softener. The carbon removes chlorine (and, with catalytic carbon, chloramine) that slowly breaks down softener resin, and the softener then removes the calcium and magnesium the carbon cannot. If you also have sediment, the full order is sediment filter, then carbon, then softener.

Water Softeners vs. Carbon Filters: What Each One Does

The two systems solve different problems, which is why people pair them.

• A water softener uses ion exchange. Resin beads swap the calcium and magnesium that cause scale for sodium (or potassium), and the softener regenerates the beads with salt brine. It does not remove chlorine, taste or odor.
• A carbon filter uses adsorption. Activated carbon grabs chlorine, many organic chemicals (VOCs) and the compounds behind most taste and odor complaints. It does not remove hardness minerals, so it will not stop scale.

Together you get soft water that also tastes and smells better at every tap. Neither one is a cure-all: carbon does little for dissolved salts, nitrates or hardness, and a softener does nothing for chemicals.

Carbon Filter Before or After the Water Softener?

On city water, install the carbon filter before the softener. Chlorine and chloramine are oxidizers. Over years they break down the cross-links in standard softener resin, which makes the beads swell, turn mushy and lose capacity. Taking the chlorine out first lets the resin last much longer.

The recommended order on a typical city supply is:

1. Schloramine (if you have sand, grit or debris). It protects both the carbon and the softener. See whether you need a sediment filter before your softener .
2. Carbon filter to remove chlorine or chloramine.
3. Water softener to remove hardness.
4. Point-of-use extras , such as reverse osmosis at the kitchen sink or UV, go after the softener. Our guide on combining a softener with UV or reverse osmosis covers those.

There is one argument for putting carbon after the softener: soft water keeps scale off the carbon. In practice, protecting the resin from chlorine matters more on city water, so carbon goes first. Install a bypass valve on each unit so you can service them separately; our bypass valve guide explains why.

Benefits of Using Both Systems Together

• Longer resin life. Chlorine-free water is easier on the softener resin, especially on chloraminated city water.
• Better taste and smell. Carbon removes the chlorine taste and odor softening alone leaves behind.
• Less scale. The softener protects water heaters, fixtures and appliances, and you use less soap and detergent.
• Whole-home coverage. Showers, laundry and every faucet get treated water, not just the kitchen tap.

Do You Need a Carbon Filter With a Softener on Well Water?

Usually not for chlorine, because most private wells are not chlorinated. Well water problems are more often iron, manganese, sediment or a sulfur smell. Those need the right equipment in the right order, and iron in particular will foul carbon quickly. Our guide on whether well water needs a filter and a softener walks through the options.

For well water, the SoftPro Elite Smart HE for Well Water handles hardness and iron up to 3 ppm when set correctly. Above 3 ppm, put the SoftPro AIO Iron Master in front of the softener. Carbon only makes sense on a well if a water test shows organic chemicals or a taste or odor problem the other equipment does not fix.

How to Choose the Right Combination

1. Test first. Find out your hardness (gpg), whether your city uses chlorine or chloramine, and, on a well, your iron and manganese levels.
2. Size the softener to your hardness and household. Set the hardness to your measured grains per gallon, plus about 5 gpg per 1 ppm of ferrous iron if you have any. Our hardness setting guide explains it.
3. Size the carbon filter to your flow rate. A whole-house carbon filter that is too small will drop your water pressure and let chlorine through.
4. Match the carbon to your city water. Chloramine needs catalytic carbon and more contact time than plain chlorine.

For city water, start with the SoftPro Elite Smart HE for City Water , or compare all options in our water softener collection .

Maintenance for a Softener and Carbon Filter

• Softener: check the salt level about once a month and keep the brine tank about half full.
• Cartridge-style carbon filters: replace every 6 to 12 months, or at the gallon rating on the cartridge, whichever comes first.
• Tank-style carbon filters: the media lasts much longer, often several years; replace it when you start to taste or smell chlorine again.
• Sediment pre-filter: change it when pressure drops or the cartridge looks dirty.

A short log of salt refills and filter changes makes it easy to see when something changes.

Frequently Asked Questions