Carbon Filter for Well Water: Do You Need One?
Number copied. Text it from your phone: 443-277-2204.
People on a well ask me, "Do I need a carbon filter?" Usually not as the first thing. The common well problems are iron, hardness, low pH, sediment and bacteria, and carbon fixes none of them.
A carbon tank earns a place on a well in four cases: a light rotten egg smell, radon in the water, a chemical a lab test found (like a solvent or PFAS), or a taste that stays after your other equipment is in. When you add one, it goes last, after the softener and before the UV light, and the carbon lasts about 5 years.
Quick Answer
Most well water homes do not need a standalone carbon filter. Carbon filters are designed to remove chlorine, chloramine, and organic chemicals. On a well there is usually no chlorine, so a carbon tank is an add-on for a specific problem, not the first tank you buy.
- What it takes out on a well. Many solvents and other VOCs (volatile organic compounds), some pesticides, radon, and a light rotten egg smell. See when a well needs a carbon tank.
- Catalytic carbon for sulfur. Every carbon tank we sell uses Centaur catalytic carbon. It handles a light smell, under about 1 ppm (part per million) of hydrogen sulfide; a strong smell needs a sulfur filter. See the rotten egg smell.
- What it does not fix. Hardness, iron, manganese, low pH, bacteria, nitrate or sediment. See what carbon does not fix.
- What it costs. Our non-backwashing carbon tanks are $1,495 and $1,695. Replacement carbon is $295 per cubic foot, about every 5 years. See which tank fits a well.
- Where it goes. Last in line: after the sediment filter, any iron filter or acid neutralizer, and the softener, and before the UV light. See where it goes.
- Test first. Each problem carbon handles has its own test. The standard well test covers the problems that come first. See which test shows it.
For a well, the 2.5 cubic foot non-backwashing tank is the one I recommend: it has the capacity a light sulfur smell and radon need, with no drain and no electricity.
What's in This Guide
When a well needs a carbon tank
A well needs a carbon tank when the water has something carbon holds onto: a light sulfur smell, radon, or a man-made chemical. Carbon works by adsorption: the chemical sticks to the surface of the carbon as the water passes through. That is also why it wears out. Once the surface is full, it stops working.
A light rotten egg smell
The rotten egg smell is hydrogen sulfide gas. First check where you smell it. If only the hot water smells, the cause is usually the water heater's anode rod, not the well, so check that first; no filter is needed for it. If the cold water smells too, how strong it is decides the fix:
- A faint smell, under about 1 ppm. A carbon tank can handle it. Make it the 2.5 cubic foot tank, not the 1.5. As I told one family with a sulfur smell, "it would be the 2.5 cubic foot 'cause you need that capacity." On sulfur water the carbon runs out sooner, about 4 to 5 years.
- A steady or strong smell, or a smell with iron. An air-injection filter with Katalox Light. It removes up to 10 ppm of sulfur, plus iron and manganese, in one tank. See sulfur filters for well water.
A carbon tank on a strong smell does not fail all at once. It helps for a few months, then runs out, and a used-up carbon bed can put the sulfur back, so the smell comes back worse than before. If you are not sure how strong yours is, the hydrogen sulfide test ($139) reports the level. The full guide is rotten egg smell in well water.
Radon in the water
Radon is a radioactive gas from uranium in the ground, and it dissolves into well water. A carbon tank is one of the two usual ways to take it out of the water for the whole house; the other is aeration. For radon I use the 2.5 cubic foot non-backwashing tank; for high levels in a family of 4 to 6, I put two carbon tanks in a row, after the iron filter.
Two things to know first. Most radon in a home comes from the soil under it, not the water; EPA puts the water's share of indoor air radon at about 1 to 2 percent, so test the air too. And EPA notes that with a carbon filter, radioactivity collects on the filter, which may make the used carbon a handling hazard and may require special disposal. EPA's proposed radon limits are for public water systems; there is no federal limit for a private well. The radon in water test ($129) gives you the number. More in how to test for radon in well water.
Chemicals a lab test found
Wells near a gas station, a fuel tank, a landfill, a dry cleaner or farm fields can pick up man-made chemicals. Activated carbon reduces many VOCs, like solvents and fuel compounds, and some pesticides. It also reduces PFAS (forever chemicals): EPA says carbon works well on the longer-chain kinds and less well on the shorter ones. None of the carbon tanks we sell is certified to reduce PFAS.
When a well test shows PFAS, my advice is to put the carbon tank in, retest, and add a PFAS system later if the numbers are still high. If PFAS is the reason you are shopping, start with PFAS water filters and PFAS in drinking water.
A taste left after your other filters
After the iron filter, neutralizer or softener does its job, some people still notice a taste or want the water polished. That is the optional carbon tank. As I put it to one homeowner with iron and manganese: "If you want the water to taste better and clean up any trace contaminants throughout the entire house, I'd go with a 2.5 cubic foot non-backwashing carbon tank. You don't need to backwash it after the iron filter."
One buyer whose well water was staining everything and tasted metallic put in the 2.5 carbon tank with an iron filter and an acid neutralizer, and wrote: "I have excellent well water, taste great."
What carbon does not fix on a well
Carbon does not remove hardness, iron, manganese, bacteria, nitrate, fluoride or dissolved solids, and it does not raise pH. These are the problems most wells have, and each one has its own fix.
| What you see or test | What fixes it |
|---|---|
| Orange or black stains (iron or manganese) | An iron filter |
| White scale and spots (hardness) | A water softener |
| Blue-green stains, pH below 7 | An acid neutralizer |
| Coliform or E. coli bacteria | A UV light |
| Nitrate | A nitrate filter |
| Sand, grit or cloudy water | A sediment filter |
| A strong rotten egg smell | A sulfur filter |
Carbon can also make a bacteria problem worse. A carbon bed can grow bacteria, which is one reason the UV light goes after the carbon tank, never before it.
Which test shows whether you need one
Test before you buy, and test for what you suspect. Our standard well water test ($199) covers 53 contaminants, including bacteria, iron, manganese, hardness, pH and nitrate, which are the problems that come first. It does not test VOCs, pesticides, PFAS, radon or hydrogen sulfide; those are separate tests.
| What you suspect | The test | Price |
|---|---|---|
| Iron, hardness, low pH, bacteria, nitrate | Well water test | $199 |
| A rotten egg smell | Hydrogen sulfide test | $139 |
| Radon | Radon in water test | $129 |
| Fuel or solvent chemicals | Solvent and fuel test (60 VOCs) | $169 |
| The basics and solvents, one sample | Advanced well test (the basic test plus solvents) | $329 |
| PFAS (forever chemicals) | Forever chemical test (14 PFAS) | $349 |
The VOC tests are not farm herbicide tests; they do not cover atrazine or glyphosate. If you are worried about farm chemicals, text me what is near the well and I will tell you which test fits.
Send Aidan your results
Text a photo of your lab report, or tell him what you smell and where. He will tell you whether a carbon tank belongs on your well and which one.
8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.Where the carbon tank goes
On a well, the carbon tank goes last, after everything that takes out iron, hardness and sediment, and right before the UV light. That way it only handles what the other tanks leave behind. From where the water comes in:
- The pressure tank.
- A 5 micron sediment filter.
- An iron filter and an acid neutralizer, if your test calls for them. I set their order from your test.
- A water softener, if the water is hard.
- The carbon tank.
- The UV light, last. It needs clear water to work, and it kills any bacteria that grow in the carbon bed.
The whole sequence, with what each step needs from your test, is in the correct order for well water treatment. If you are adding carbon and a softener together, see carbon filter and water softener.
Which carbon tank fits a well
For most wells, the right tank is the 2.5 cubic foot non-backwashing tank. A non-backwashing tank needs no drain and no electricity. Backwashing does not make carbon last longer, because carbon holds what it adsorbs; it only rinses out dirt. So a backwashing carbon tank is only for a well where carbon is the only filter and the water has heavy sediment or some iron.
| Tank | Price | Who it fits |
|---|---|---|
| Clack 2.5 cubic foot, non-backwashing | $1,695 | Most wells, 2 to 10 people, up to about 17 gallons per minute. The one for a light sulfur smell or radon. |
| Clack 1.5 cubic foot, non-backwashing | $1,495 | Smaller homes (2 to 4 people), up to about 10 gallons per minute. For taste after your other filters, not for sulfur. |
| Fleck backwashing, 1.5 or 2.5 cubic foot | $1,895 or $2,495 | Carbon as the only filter on a well with heavy sediment or some iron. Needs a drain, an outlet, and a well that supplies the backwash flow. |
The carbon in each one is replaced about every 5 years, sooner on sulfur water. Then the old carbon comes out and new carbon goes in; Centaur carbon is $295 per cubic foot. If you are buying a softener too, we sell the 1.5 tank with a 48,000 grain softener ($3,195) and the 2.5 tank with a 64,000 grain softener ($3,795) as carbon and softener packages. The full comparison is backwashing vs non-backwashing carbon filters, and for every model side by side, see the best whole house carbon filter.
Installing a carbon tank on a well
What ships with a non-backwashing tank: an empty Vortech tank, the Clack in and out head with a bypass valve, the Centaur carbon in separate boxes, and a funnel to pour it into the tank at install. Plumbing fittings and drain tubing are not included; the connections are 1 inch male thread, which works with PEX, PVC, CPVC or copper.
I recommend having a plumber put it in, and I'm a phone call away for your plumber. A non-backwashing tank on its own has no drain line and no electricity, just an inlet and an outlet, so it is about an hour or two of a plumber's time. On a well it usually goes in with other tanks; that is a bigger job, with each tank in order and a drain line for each one that backwashes, so ask for a plumber who has installed water treatment before. A backwashing carbon tank needs a 1/2 inch drain line with an air gap and an outlet for the valve. If you have done some plumbing and would rather do it yourself, text me at 443-277-2204 with any questions.
My three-minute video on carbon tanks
In this video I go over what a whole house carbon tank removes, how long the carbon lasts, backwashing vs non-backwashing, and when a well needs an iron or sulfur filter instead.
Frequently asked questions
What are the disadvantages of an activated carbon filter?
It runs out, and nothing tells you when; the smell or taste coming back is the usual sign. A carbon bed can grow bacteria, so on a well it goes before a UV light. A used-up bed can release what it held, which is why a carbon tank on strong sulfur water makes the smell worse after a few months. And it does nothing for hardness, iron, bacteria or nitrate.
How much does a whole house carbon water filter cost?
Our non-backwashing tanks are $1,495 (1.5 cubic foot) and $1,695 (2.5 cubic foot), and the backwashing tanks are $1,895 and $2,495. Add a plumber's time and the fittings, which are not included. After that, the cost is new carbon about every 5 years, at $295 per cubic foot; there is no salt and, on a non-backwashing tank, no electricity.
How long does a catalytic carbon filter last?
In a whole house tank, about 5 years, sooner on sulfur water or with heavy water use, and a little longer if you use less water. A small cartridge on sulfur water can be used up in a few weeks. Backwashing does not stretch the life of the carbon.
What does a catalytic carbon filter do?
It adsorbs chemicals like regular activated carbon, and its surface also speeds up chemical reactions: it breaks down chloramine faster than standard activated carbon, and it converts hydrogen sulfide to sulfate, which has no smell. The carbon in every tank we sell is Centaur, a catalytic carbon made by Calgon Carbon from bituminous coal. For a side-by-side, see catalytic vs standard activated carbon.
Aidan Walsh
Co-owner & Residential Water Treatment Specialist, Mid Atlantic WaterAidan Walsh has spent 32 years in residential water treatment, the first stretch of it installing and servicing well systems before Mid Atlantic Water became an online supplier. Mid Atlantic Water is a family company; every recommendation on this site is based on what actually failed in the field and what fixed it. If you have a question this page did not answer, call 800-460-5810 or text him at 443-277-2204.
Aidan answers calls and texts 8 AM to 5 PM Eastern, every day.Number copied. Text it from your phone: 443-277-2204.